you bought it and NOW you want to know if you can get a better deal on it? and you "think" it's missing "that aftertouch thing" ... you sure have a lot of money to burn don't you?
at least you bought a decent keyboard, but damn, if I were spending that much money I would research enough to justify paying that much for anything. Aftertouch, btw, is how much pressure remains on the keys when you play them. Here's some more info on aftertouch.
I'll refrain from talking about the MM8 since I've never actually seen one, but I can tell you that fiscally, if you just want midi sequencing, recording, and composing, and you already have a decent computer, you don't have to pay a single dime. You might be able to sync up the MM8 with your PC and some free software [and a few bucks for a midi interface with cables, unless your keyboard has USB out on it]. I'll tell you how if you're interested. Still, I don't want to get you on the wrong track if the MM8 has decent sequencing built into it.