Better Music System works just fine. Make sure you have all the prerequisites, of course, and configure the ini (if necessary, or desired) as you wish.
Oh, and add a bunch of mp3 tracks to the various folders, again as you wish. Otherwise, the mod ain't much use.

edti: Well, actually, it does a few other things by default, which I do appreciate. So, to be fair, even if you don't add any tracks, although you'd be wasting the bulk of the mod, some of the side-effects are quite neat, IMO.