Well, I would suggest looking at some names for ambience sounds (usually named something like zone_ something or other, and take away the .wav after it, so you'd end up with for example: zone_nebula_edge.

Then in your zone entry, add to the bottom

music = zone_nebula_edge

and you should then have music in there, of course, you could just overwrite existing music with your own, but I'd suggest finding the adding music tutorial. Then you might have a better idea on how to add new music.