go to the game's data files, and find "Audio", if you don't find one, create one.
next, put your mp3 in there and run the game.
click the button that icon: music note
select whatever room you want, not play button, but the right side of play button. It should give you a song you add in the game data.
select the song you want.
don't forget, click the "use this playlist" checkmark.
try it.
-Ellio :l