I'm using BG TotSC (part of the 4-in-1 boxset) with the latest official patch, and a SB X-Fi card. And I have this really annoying problem. Music rarely starts up when I enter a house, an area on the world map, or any place where the loading screen comes up briefly. Every time I enter a different area, I have to quicksave in order to "kickstart" the music because it won't play on its own. And for some reason it always plays after doing a quicksave. Also, if music is playing and I do a regular save through the options menu, it stops playing.
And before you ask: I have EAX disabled in-game AND through my soundcard control panel (both were On before). And it makes no difference. So I doubt it has anything to do with this problem.