As much as I like the music, I generally have my own music (DI.fm Trance channel) playing in the background, and would rather have that as music.

Anybody know if I need to use a switch, or is there some hidden option in the game itself?

I don't think it is possible. On the the web page (http://www.robitstudios.com/) Stephen Orlando claimed that he would add this possibility but that was Nov. 2011 so I guess he forgot about it.

Well, you can mute the game with audio mixer but you will lose the sounds as well so I guess it's not the best solution.