OK well, you got me curious with this question myself. So after about 20 minutes of playing around, this is what I figured out.
Well, if you look in:
You will see 3 files:
I checked these first. I was able to use GoldWave to open them interperating as wav files, but all the sound runs too fast or too slow. I could definitely hear that they are all the voices and sound effects, but I'm not sure exactly how they are compressed. I opened as Raw PCM signed 32 bit, big endian stereo 96000Hz for the "Non-Localized" files (SFX) and little endian for the "English" (Dialog)
But the answer to your question is the "Music.meg" file located in:
I didn't notice this file untill after I did what I mentioned above
and went back to try and figure out what I missed.
Music.meg actually appears to be an Mp3 192 Kbps, 44100 Hz Stereo 63 min 8 sec, so it certainly should be easy enough to create a replacement. I would recomend using some kind of audio mixing software. The breaks that seperate parts in the music definitely are queues that are triggered by events in the game. I.E. when a battle begins you hear the "Tie Fighter Attack" theme. You might want to keep the time queue so it works well.