I think you might be on to something, hszp.
If we define certain "flags", maybe they could later be used to change the ambient music in certain ways? This wouldn't have to be used at first, but there appear to be people here who are interested in creating additional music tracks... also, maybe it could be possible to change the music's pitch and/or tempo according to certain flags?
think about this: geoscape music changes to a slightly dramatic "alert"-type music when a UFO appears. you send an interceptor, and the music changes to a more "dramatic/battle" type of music. as your interceptor closes in on the UFO, its radar detects a second UFO - the music increases slightly in tempo (doesn't even have to be a noticeable difference... it will have a subliminal effect). if you happen to detect even more UFOs, each new one will increase the tempo even further... in heated air battles, this would probably increse the player's adrenaline levels without him/her ever noticing

the same would happen in the battlescape.
I would think of flags for these "situations":
geoscape:
- UFO detected (wait, does the music already change for that? I'm not sure and can't check right now)
- UFO shot down
- number of UFOs visible on the geoscape
- number of interceptors in the air
in dogfight:
- number of shots fired (?)
- amount of damage to participating interceptors
- amount of damage to UFO
battlescape:
- number of aliens visible in the battlescape
- number of soldiers wounded
- number of soldiers killed in this battle
- number of aliens killed in this battle
- number of soldiers with morale below certain threshold
- number of shots fired during turn (?)
I'm sure there's many more things that could influence the music... but do you think this could be possible at all, Warboy? How difficult would it be to include more music tracks? And would it be possible at all to change pitch and tempo according to "situations" as above?