Different music for each civilization

[Markezuma]

I'm looking to make a little mod where the background music is different for each civilization you play. i.e., If you play as China, you'll hear Chinese music for each era. I've been poking around the xml files and the python source and I've found where all the soundtrack files are defined and also where all the era soundtrack songs are defined. However, I can't find where the music is actually played. I was wondering if anybody can point me to it, or if this modification is even possible without the SDK (I'm assuming it is, though). Any help is greatly appreciated. Thank you!