Well, I'm sure you know this by now, but for others- Although the music is good, it doesn't play for most of the game. One mission has its unique tune, the rest only get the one that plays at the briefing, and only then. There's also music in cutscenes, the main menu and credits. It's not a compatibility issue or something, I played the game when it was pretty new.

The soundtrack provided by GOG doesn't have everything, though.