It's an allright idea, but not very easy/impossible to implement. Note, that every map the gang outposts have is the same. So Gang XY who has an outpost base has the same map as Gang ABC who has also an outpostbase etc. And - the soundfiles are mostly attached to the maps. You could only write a little program, to play music XY on your outpost map.
On the other side, the devs could place a music file global for those maps. But which music should be played there?