I seem to already have this option. System config -> Master Volume -> Off.

Queue up music I like, and listen to that instead of game music. It's not that the FF music is bad - no, far from it, the FF music is excellent. It's just that hearing the same score, even an excellent score, over and over and over becomes quite boring to me. Sometimes I need something fresh instead of the thousandth repeat of a zone theme.

...I get what you are saying, though. A portable Orchestrion-type device to select game music anywhere and anytime in-game would be fun and cool.