APZX

Short concise answers first, and then I'll follow up with technical geeky mumbo jumbo.
1 - Technically, a line output from your audio interface should be able to drive many line inputs because they use Impedance Bridging, which relies on the core assumption that both the line output and line input are done properly. Though to do this does require have cables or a box that allows you to split the signal. However, if you have multiple outputs then it affords you more flexibility in how you can set things up. 
2 - I don't see any reason why not. Just well made cables I suppose. You know for cable longevity and reliability. 
All right time for the technical geeky mumbo jumbo if you want some further explanation on things. 
Lets talk about that headphone output on the Roland Rubix 24, which Roland actually gives a maximum power specification (well at least sorta kinda, but better than nothing). Anyway, so a headphone output is really just a mini power amplifier because at the end of the day all a pair of dynamic headphones (like the two you listed) are just tiny speakers. So, Roland specifies the output power as 20mW into 47 ohms. You can estimate the amount of SPL your headphones will have based on this. It isn't perfect and you could sit down and try and do fancy mathematics to get at a more concise answer, but this is just quick and dirty. However, simple cross multiplication should "ballpark it". So, for the Sony MDR-7506 headphones you can expect that about 27mW maximum will be on tap. This is calculated by the classic (20mW/47 ohms) = (X/63 ohms). From here you get (63 ohms * 20mW) / 47 ohms. The ohms cancel out and you're left with 26.8mW. At any rate the MDR-7506's have a specified sensitivity of 106dB/W/m. This would give a peak SPL in excess of 120dB SPL. So, I'd say there is probably plenty of room there. Next up are those Beyerdynamic DT 880 250 ohm headphones. So, these are rated at 96dB/W/m (not stated like that, but at any rate). So, doing the same trick as before the Roland unit should produce around 106mW into the DT 880s. This gives a peak SPL around 116-117dB. Now, these numbers are estimations on the maximum SPL that you can expect from the Roland and can be eaten up quite quickly by very big and powerful transients. So, unless you want more volume I've never really understood the point of headphone amps 99% of the time personally, but I digress. Most of the time headphone outputs simply use an inadequate device for the output stage without enough bulk energy storage (big capacitors on the power rails). My best guess is that the Roland is probably using an "okay" opamp as the output stage. I'd be willing to bet that the headphone output on the Roland is either a single JRC4558 or two JRC4558s that are paralleled up. I doubt that they're using anything better, and for a whole mess of reasons this part is basically barely & adequately passable part for the job, but again I digress.
This then I guess begs the question why would I say much about that? Well see the output is probably just an opamp anyway. This means that it'd have no problems driving any line input. It won't be balanced and it will probably be noisier than a dedicated line output given that it is being used as a power amp, BUT there is nothing "technically" wrong with using it that way. Not best practice of course. 
I also feel it necessary to say something about the impedance balanced output. Really the trick here is to understand what "impedance balanced" actually means. In a nuthsell this means that the cold lead or "- lead" is not actually driven by anything, but instead presents the same "impedance" to ground that the hot lead or "+ lead" presents. This will eliminate most things like ground loops and hum, but not much else, which for most things is an acceptable compromise in cost. The other common option is to drive both the hot and cold leads and this provides much better rejection of all sorts of things, but it is more costly. Why use two opamps, four bypass capacitors, and five resistors when you can use one opamp, two bypass capacitors, and six resistors. Takes less board space and costs less overall to do the single opamp. 
Hopefully, you found something useful in there.

@Dextastic
You don't have use the gate as a full on gate either. Just use it to turn down the sustain part automagically
 

I guess it would be the way that instruments are placed. You can have extremely short reverbs that'd do pretty much what I'm hearing. But you are right there isn't any reverb there. 
Some tips. The single largest issue you have going on that I can hear is that everything is fighting for the number one spot. That just doesn't happen. For one sound to have something it has to take away something from another. Choose one sound you want to be the focal point. Then make everything fit around that one sound, for example the strings. Now, the strings aren't going to be your instrument here. So, what is another big focus? How about those timpanis (they sound like them or they could be taikos, but the attack is different). There is a lot of sustain on them. You've now got a choice to make. Do you just let their sustained portion run into one another creating a constant rumble? Or do you space hits so that the sustain of each hit ends before the next hit? Or do you try and quell the rumble in the mix? Of course you still have to consider the rest of the percussion. The snare? Where is it going to sit in relation to the timpani and the strings? What about the hats? How are they going to interact with the strings, timpani, and snare? How about that guitar (again I think it is a guitar, almost like a picked bass)? How are you going to integrate that in with the rest of the instrumentation? These aren't just mix focused questions, they are compositional questions first and foremost because the start of a solid mix is where the composition has everything basically where it ought to be. Sure some sounds might need a nudge or two, but in general things should be working in the composition. Well before you ever hit the notion of mixing. 

You're more patient an individual than myself lol. 

Got my entry up. The one thing I've always admired about the Metroid Prime OST is its ability to be both beautiful and scary at the same time. 

I rather like Wave Alchemy's stuff. They have some free stuff, and they have a free EDM oriented kick drum pack, Club Kicks. Give a look to their free samples as well. Some pretty solid stuff there including some quite nice 707 samples (quite an awesome kick honestly), some samples of a Vermona DRM (slightly biased as I have one of these myself, but excellent samples), and MS-20 Mini (these are some pretty darn solid and tight samples). 

Frankly, it is kind of a crapshoot. It isn't like in mixing where you can make a very good mix just using the bundled with the DAW. However, with synths or samples you've unfortunately gotta spend $$$. It kind of sucks to say it, but it is the truth. I mean I don't do orchestral music because I find the libraries 1 - Too Big 2 - Too Expensive and 3 - Too complicated. And this is coming from a guy who loves modular synths with more knobs than you can throw a stick at. But that doesn't mean everyone should be all synths all the time. I enjoy listening to well crafted orchestral takes on songs, and I like using real strings from time to time myself, but then again I kind of obfuscate them in my tracks because I just want the hint of realism and their additional qualities rather than having them as my main focus. But I do have some quite nice soundfont pianos because there a couple of good ones that are free. The best probably being the Salamander Grand Piano. But I digress.
If you recognize their intent then I do feel it is probably best to let them know that with their current tools they're unlikely to achieve what they want or are going for. This isn't really a disservice, but frankly a truth. Sure it is a bit cold, but what are you to do? I mean you don't have to come out and be a total downer when you say it. A lot about how you'd approach the situation is really just how you say it. At least that is what I've found. 

I've already quoted this once, but I've got more thoughts on it after sitting on it for a day.
Yes, I do my best to avoid telling people to "get better samples" in their music, but one does need to be careful not to step on the intention of the artist, either. On the one hand it sucks to be told "You can't make it without forkin' the money!", but on the flip side people don't like being told "You can't do something with the tools you've got, but perhaps this different idea you didn't envision would work", either; most people don't like being told how to compose something. There does come a point where you do either need to pay or have some solid musician connections to achieve your artistic vision, unfortunately, so I'd be doing people no favors to pretend otherwise.
More or less just thinking aloud on here, but telling people what they should be composing is definitely overstepping my bounds, too, though in a different way than telling them they need to spend money does. Curious what a good compromise is for something like this - perhaps acknowledging you understand what they want to achieve, explain what would be necessary and give an alternative if the necessary method proves out of reach?
Food for thought.

That there I feel brings into question a larger more overriding notion that is merely being glossed over here. You even mention a good example yourself, Trance versus Jazz. I'm a Trance head for the record. So, repetition in Trance is very much a thing, and is really a core tenet of the genre as a whole. However, if you go listen to Trance you'll find that it is actually less repetitive than you might think. The texture of the track is varied and modulated throughout. Someone who listens for chord changes and progressions is likely to be bored as a result of this. I think Trance is actually kind of a bad choice in this comparison and would instead choose Minimal as it is far more repetitious, or you could even throw Ambient in there. Even then those two genres have their own kind of movement to them that should be taken into consideration. To simply ignore this is missing a core principle of the genre at hand, and not looking at things from the appropriate perspective. Just my $0.02. 

First off, I do want to point out that what @Gario said in here seems to just be a typo. I listened through the track, and I think he just meant 0:18 - 1:36 vs. 1:36 - 2:54. THAT would be a pretty significant repetition and THAT makes a lot of sense to me. And it isn't just the idea of repetition that's the problem---it's the collection of textures, expression, contour, . . . that feels too same-y the second time through. If that wasn't apparent the first time, @HoboKa, hopefully that clears something up.
Yes, I do see what you mean there. And that boils down to, "what is the point of this particular music?". The purpose of video game music WITHIN a video game is to keep the gameplay exciting, match the mood, what have you, and if it had an ending at an improper moment in the gameplay, that wouldn't feel right. And so, looping is an easy way to make sure that doesn't happen. That's fine, in that context.
With "actual music", i.e. music that is meant to be listened to as complete, standalone tracks, satisfying endings are preferred, and repetition is disfavored. Of course, repetition keeps familiarity with the musical content, but eventually it gets taxing, and the Judges regard repetition in a general manner, trying to predict how long someone would need before they skip to a new song, let's say. And that varies from Judge to Judge---someone who writes trance music might be more numb to repetition than someone who writes jazz. There are inherent assumptions as to how repetitive is too repetitive, and that's really the contention you have here. A non-Judge might not be actively watching out for blatant copy-paste, whereas mods and Judges would (or should) actually keep that in the back of their mind.
That's a fair remark. But even Simon himself has gotten nicer over the years, in case that wasn't clear from the more recent America's Got Talent appearance he made this year. Along similar lines, Liontamer has also been passing stuff more recently that I might personally not be totally in agreement with, but that I would argue is a good thing (from the perspective of the listener, that is). I've never met him face to face either, but I definitely enjoyed the OCR Podcasts I managed to get onto with him there, at least.
In general, as I keep suggesting to all the aspiring or struggling composers here, you gotta have a thick skin. Just keep in mind that you gotta read through the Judge comments with some scrutiny in the sense that they're made from a human's perspective, and differences in perspective will arise. Fix what you agree with, and see if you come to a better agreement.
It's an iterative process (and here I'm referring to any remixer), and by being self-aware and honest with yourself as I mentioned, you can eventually spot your own mistakes and improve on those without simply submitting as soon as you get the chance (not trying to accuse you here). That will give you a better chance than making small tweaks and subbing again with little community input----that's what mods are for!
Hey, I'm glad you got that out of your system (or some of it anyway). No matter what though, asking more questions, IMO, is better than simply getting frustrated internally and keeping it to yourself. I don't speak for the community, but I think that as a whole, we are generally willing to put up with "rabblerousers", and "shit-shows" as you put it.

@Dextastic
I've got nothing against Rock or Metal, heck I love me some Prog or Psychedelic Rock and some Metal stuff. It is just that really most of the time it is the people behind the guitars rather than the guitars themselves that I have an issue with. Not trying to imply anything just a "general observation". 
Also, no problem giving some techniques for dealing with things in a mix. I've done a few Hard Rock and a couple of Metal Mixes and there is definitely some different things than you might think. Something else to consider when mixing is that tricks that you may have used in one mix may come in handy for a mix that is completely and utterly unrelated in both genre and style than where you learned it. You'd think that  I'd never turn to distortion in a non-rock/metal mix, but surprisingly it comes in handy in all sorts of places. In particular I like using it on bass too make it easier the ear to find it in the mix if it is quite dull. 

@Dextastic
With the compressor pretty much, but you'll need to adjust based on taste and even play with different compressors as they're attack and release curves will change the way the sound behaves. Just gotta experiment a bit. I can tell you that for this particular application I really really like vladg's Molot. I know it is written in the Cyrillic alphabet, but there is an English option and I like to do this in the "Alpha" mode because it isn't quite as aggressive. It is preference and I've used different compressors for the application just based on various things from changes to the timbre to fitting better in with the other instruments. 
Compression in general is quite a complex topic and it'd take me way too long to explain in any reasonable detail about how it works or the various ways to use to manipulate space or even forcing one without a sidechain input to react in an almost dynamic EQ kinda way. But with that being said you've really just gotta experiment with it to find something that really works for you. I can tell you that I have a lot of compressors because I find unlike EQs I can get more color out of them and that is typically what I end up doing on a lot of sounds. Rather than using them strictly for mixing. 
I say compression on the guitars because even though distorted guitars are already quite compressed it isn't the end all be all to further coloring them with compression  Much to learn about that you do! But some things you can try to give the guitars some more weight. Put on a different hat for distortion for a minute. Think of distortion as a way to generate new and extra harmonics that you can then manipulate to your advantage. For example you could try some frequency selective parallel distortion to add in some extra girth that you can then mix in with the original to give them more heft if they're missing it. Kind of like the old trick of gating a tone generator from a kick to make it beefier in the mix. Since you have 4 guitars in this particular case then I would look at doing something a bit different personally. I'd take two of them and hard pan them and leave them mostly alone (EQ, compression, etc.) but pan the other's about midway left and right then play with distortion on them and make those heavier sounding. This would likely widen the mix with two different guitar layers at two different stereo positions, but would also have the effect of making the center seem "heavier" and leaving the sides "lighter" further adding to width without really sacrificing any mono compatibility  
As for the synths, I mean they kinda work. The brass is actually a pretty good sounding brass stab, but it sounds like it came from a ROMpler of some description. I like the piano quite a bit, and I love the sync lead but it is so buried and overshadowed by everything else in that section that it kind of loses its impact  While this may sound kind of biased or such, I really really dislike guitars lol. Not because there is anything wrong with them, but just because I'm not a guitar guy and everyone talking about them makes it sound like there are humongous differences between ancient humbucklers and modern ones. Look Solid body vs Hollow Body? Easily understandable differences in sound. But I feel arguing about a 139048 year old humbuckler is like the synth guys saying that there is a huge difference in the way a 50 year old Minimoog sounds versus a clone from like Studio Electronics. Look is there a difference? Probably, but is it worth all that money for it? Probably not. I'm a synth head and I love synths. It is easier to impress me with guitars than it is with synths. Suuns' 2020 (warning epileptic seizure warning) has a guitar sound that I love because I've never really heard it before and plus it is super creepy and unsettling. The bass is a synth and super dark and brooding. Both of those sounds impress me. Mord Fustang's Lick the Rainbow (terrible name I know), but this has quite a few synth sounds that just impress me. Still trying to figure out that bass sound myself. So much breath and life in that. Your synth sounds aren't bad, but if you want something to really show you what is possible with just one synth, then look no further than KVR's One Synth Challenge (I've entered a few myself) and let me tell you some of the sounds people are able to coax out of these synths is simply astounding. 

@Dextastic
I've got nothing against Rock or Metal, heck I love me some Prog or Psychedelic Rock and some Metal stuff. It is just that really most of the time it is the people behind the guitars rather than the guitars themselves that I have an issue with. Not trying to imply anything just a "general observation". 
Also, no problem giving some techniques for dealing with things in a mix. I've done a few Hard Rock and a couple of Metal Mixes and there is definitely some different things than you might think. Something else to consider when mixing is that tricks that you may have used in one mix may come in handy for a mix that is completely and utterly unrelated in both genre and style than where you learned it. You'd think that  I'd never turn to distortion in a non-rock/metal mix, but surprisingly it comes in handy in all sorts of places. In particular I like using it on bass too make it easier the ear to find it in the mix if it is quite dull. 

@Dextastic
It doesn't sound all that bad. In fact I rather like the transients on the drums quite a bit. Though if I may make a couple of suggestions. First, while the transient is important on drums in order to prevent the cymbals and the like from being "too" powerful in the mix you may consider actually toning down the sustain portion. You can achieve this in a few ways. Transient Controller can work well in certain situations. Another way is to use a compressor and just crack down on that transient quite a bit and not really use much makeup gain, then apply some EQ (typically 4-8KHz) to bring the transient back. There is also the gate that opens up on the transient but closes on the sustain. You can also play a bit with multi-band compression or even dynamic EQ. Just depends on your desired end result. Second, with the drums you did a solid job of imprinting their space in the mix along with the guitars. However, when things get "fuller" you basically completely run out sonic space in those sections and don't really have separation nor clarity between the various elements. No real tricks here other than good ol' listening and trying to figure out what needs focus and possibly rebalancing the mix on the fly with automation. Bonus bit, the guitars could do with a bit more weight and get on those guitars with some characterful compression. Otherwise pretty darn solid. 

@Dextastic
With the compressor pretty much, but you'll need to adjust based on taste and even play with different compressors as they're attack and release curves will change the way the sound behaves. Just gotta experiment a bit. I can tell you that for this particular application I really really like vladg's Molot. I know it is written in the Cyrillic alphabet, but there is an English option and I like to do this in the "Alpha" mode because it isn't quite as aggressive. It is preference and I've used different compressors for the application just based on various things from changes to the timbre to fitting better in with the other instruments. 
Compression in general is quite a complex topic and it'd take me way too long to explain in any reasonable detail about how it works or the various ways to use to manipulate space or even forcing one without a sidechain input to react in an almost dynamic EQ kinda way. But with that being said you've really just gotta experiment with it to find something that really works for you. I can tell you that I have a lot of compressors because I find unlike EQs I can get more color out of them and that is typically what I end up doing on a lot of sounds. Rather than using them strictly for mixing. 
I say compression on the guitars because even though distorted guitars are already quite compressed it isn't the end all be all to further coloring them with compression  Much to learn about that you do! But some things you can try to give the guitars some more weight. Put on a different hat for distortion for a minute. Think of distortion as a way to generate new and extra harmonics that you can then manipulate to your advantage. For example you could try some frequency selective parallel distortion to add in some extra girth that you can then mix in with the original to give them more heft if they're missing it. Kind of like the old trick of gating a tone generator from a kick to make it beefier in the mix. Since you have 4 guitars in this particular case then I would look at doing something a bit different personally. I'd take two of them and hard pan them and leave them mostly alone (EQ, compression, etc.) but pan the other's about midway left and right then play with distortion on them and make those heavier sounding. This would likely widen the mix with two different guitar layers at two different stereo positions, but would also have the effect of making the center seem "heavier" and leaving the sides "lighter" further adding to width without really sacrificing any mono compatibility  
As for the synths, I mean they kinda work. The brass is actually a pretty good sounding brass stab, but it sounds like it came from a ROMpler of some description. I like the piano quite a bit, and I love the sync lead but it is so buried and overshadowed by everything else in that section that it kind of loses its impact  While this may sound kind of biased or such, I really really dislike guitars lol. Not because there is anything wrong with them, but just because I'm not a guitar guy and everyone talking about them makes it sound like there are humongous differences between ancient humbucklers and modern ones. Look Solid body vs Hollow Body? Easily understandable differences in sound. But I feel arguing about a 139048 year old humbuckler is like the synth guys saying that there is a huge difference in the way a 50 year old Minimoog sounds versus a clone from like Studio Electronics. Look is there a difference? Probably, but is it worth all that money for it? Probably not. I'm a synth head and I love synths. It is easier to impress me with guitars than it is with synths. Suuns' 2020 (warning epileptic seizure warning) has a guitar sound that I love because I've never really heard it before and plus it is super creepy and unsettling. The bass is a synth and super dark and brooding. Both of those sounds impress me. Mord Fustang's Lick the Rainbow (terrible name I know), but this has quite a few synth sounds that just impress me. Still trying to figure out that bass sound myself. So much breath and life in that. Your synth sounds aren't bad, but if you want something to really show you what is possible with just one synth, then look no further than KVR's One Synth Challenge (I've entered a few myself) and let me tell you some of the sounds people are able to coax out of these synths is simply astounding. 

Honestly, I've looked at the PRC and MnP things lately and I just haven't jived at all with any of the sources  Short of doing a straight cover for them, I dunno. I at least try to remember to vote for them because that is the least I can do even if I don't jive with the source. 

Dextastic,
Basically, the snare to me is just a pop. I mean if I listen a bit more closely I think I get where you were going, but I mean in context the drums sound too wet except for the hi-hat which may be what is throwing me off. Still I just don't like the snare. I'd say if you want that kind of big wet snare then gate the reverb on it. If that is the natural sound of the snare then I'd work on de-reverbing it so I could control the amount of reverb present myself. Ultimately, the issue I have is a personal thing. There is nothing wrong "technically" with the snare. 
Silverpool,
The hi-hat just lacks movement. You use FL, right? Go to the piano roll and select all the notes for that hi-hat and press Alt+R. Deselect Pattern as that will cause all sorts of funkiness that you're not after. Then select Levels. Under there select Bipolar and then move the "Vel" and "Pan" knobs around, also press the "Seed" buttons and this will give the hi-hat some very slight movement. That is the kinda thing I'm talking about. Takes about 30 seconds.

I tried something, but my issue was getting the main melodic motif to play nice with the rest of my track in a way I liked. Never happened  Otherwise mine is 90% done lol. Anyway, looking forward to giving a good listen to what folks have done with it. 

My submission is up. Not my best work, but a fun little source nonetheless. 

It is getting sorted out, just not before the weekend because there are a lot of logistics involved. I've got a temporary window unit for the bedroom so I can at least sleep comfortably lol. This isn't all that bad all things considered really. More of an annoyance. I believe a corollary of Murphy's Law is being invoked that states something along the lines of if there is a worse time for something to go wrong, it will happen then. 

Well it probably ain't gonna happen or a "finished" product at least and here is why. So, last night around 8PM my AC unit decided it had had enough. Well turns out that when things fail "things fail"! That means I've gotta get pretty much the entire system replaced  which means I really won't have any free time for the next few days because there is an absurd amount of work that has to be done. Thank you southern summers. Was 98F today and I'm pretty sure the house is about 90F right now. 

Still got a couple days worth of work for it. Composed, just needs mixed. I'll see if I can get it Friday though. 

Bah stupid work, I wanted to get my bonus up in time
Anyway, solid stuff guys! Took a few listens to figure out who to vote for.

Next round is up!
 

Results
APZX got 1st with 13 points. HoboKrap got 2nd with 12 points. Dex got 3rd with 11 points Silverpool got 4th with 7 points APZX PM me for the round 76 entry!
Comments
Mirror, mirror on the wall it seems that APZX is the most MnP of them all.  Because it's..........Smash Bro's Brawl??  It rhymes.  Congrats dude, hit me up with entry 76 when you are able