Methinks we need DEATH METAL on occasion.
It'll be easier for people to see it then for me to describe it.
Download the nord mod and install it and then go into your Skyrim/data/music folder area and you'll see what those files look like, what they're named, the extensions, subfolders, and so forth.
I'm not sure if that's the form that HAS to be used or not. I don't know if the game insists on .xwm files and name structure like that or not.
Once that's determined up or down then, hell, anyone can use any music they want.