Thanks SO much for providing additional explanation. In terms of your comments on soundscape and voicing, I can see that my problem (and limitation) is a lot worse. I actually only have one instrument (an alto), but I write multiple parts based on to recreate some of the other sounds. For the bari sound, that's really just the alto shifted down an octave in my DAW. (In some of my earliest covers, I would try to do something similar to simulate a soprano sax, but going up in tone in a DAW sounds far worse than going down.) The tenor sound is just an alto part playing lower notes.
In general, when I arrange, I try to arrange any bari parts as if it can take the lowest parts from any original (e.g., bass). But that's apparently not working out so well, since as you say, I'm just missing bass tones.
Yet, that was originally my plan -- to use sax for as much as possible (excluding drums). Would you say that is just unworkable in the long term, and I should arrange to have bass (even if I have to get a VSTi for that)? I also got a clarinet to maybe add something different to the higher end, but learning how to play clarinet is a lot more difficult than I planned (haha).
I can hear the tuning problems now for the bari, so I can work on that.
I'm going to think and study really hard on your middle paragraph here for the specifics as to harmonic context, since I know that's stuff I need to know, but it's still all a foreign language to me now.