I've had 0 luck on this so far (aside from you fine people and your helpful posts ^_^). I desperately want to be able to do this, but it's seeming more and more like unless I spend lots of time learning about hacking, I'm never going to be able to.
The closest thing I remember getting to what I want was when I used, I believe (it was quite a while ago), sappy.exe to export a midi, and saw that it had an "include samples" (or something similar) checkbox. But whenever I checked the box and tried to export, it would crash. It would export a midi if I didn't check the box, and the midi would match the actual tracks from the game exactly, but it would play using my sound card's instruments rather than the game's.
It's frustrating because I just can't seem to get a perfect copy of the instruments just by starting with a generator in Garageband and tweaking settings, despite how extensively I've tried. I've had a look at the two links on "Music hacking" on the romhacking site, but none of the articles are specifically on Megaman Battle Network 6, and as your site even says music formats vary wildly between games.
I just don't know what to do. Please help, if possible.