I think one of the DATA files sets the radio station each ped prefers & that's cross referenced against CARGRP.DAT (the
file that determines what cars are driven by what groups. Emphasis on I THINK.
In a script edit, you may be able to set radio stations in car spawns, but i haven't dug into them that far yet.
Something just occurred to me. In an IPL edit, you can set an audio zone where something plays all the time & I think
there's a setting to user tracks (I've heard them in the wardrobe, that one is set to favorite station). Figure out the XYZ
co-ords for SA & make one huge audio zone for the whole map so you'll hear it in a car, on foot or inside.