I've been trying to put in "classic" music for a while... I'm no modder, but I figured out that the music is used from the sounds .bsa in .ogg format. For example all daytime desert exploration music is in Sound/fx/mus/inc/day. All the tracks are pretty much cut up into 10 second snippets. I've tried putting in custom music (e.g. redding theme) but it just ends up layering on itself many times (i guess due to length being over ~10 seconds). The game chooses these snippets randomly. If anyone could figure this out, it would be really awesome. This game definitely needs more F1&2 music.