I agree with RB about Xbox stuff being streamed. Most Xbox stuff I've looked at have used wma-like formats for music instead of MIDI/synth music.
Also, having used an Nforce2 motherboard for over a year and a half, I'd say that Soundstorm's MIDI support isn't exactly great. The MS DX soft synth often sounds better, even if you can manage to get Soundstorm to load a good soundfont. It's a great chip for game audio, but not for MIDI.