I'm an old-school MMO player, and have long been in the habit of turning ingame music way down or all the way off so I can hear the game's sounds (which is real handy listening to audio cues when someone/something is trying to sneak up on you.) One of the first things I do in almost every game I play, MMO or otherwise, is to go into settings and turn the music down to 20% at most, and sometimes all the way off. I like how Elite allows you to "cherry pick" which tracks will play, so for instance I can turn off combat music which I view as more of a distraction during a fight than a benefit.
On the rare occasions that I do have other music playing, it's usually instrumental (light jazz, classical, etc.)