Music trigger

How do you make a trigger where you have a little area and there are circles of power and each one you step on plays a different song and when it leaves the area the song turns off.

Also, I've imported a few songs but putting them in there makes the map to big to play. Can I make these files smaller in any way with some type of program?

a unit enters region - play sound file
a unit leaves region - stop playing sound file

something like that