the msu in snes games works with a hook in the audio play/stop/trackselect routine! If you can find this, you can add a hook to the a free space in the rom and load the msu needed asm. Here you can load the tracknumber like 1C and the msu asm will check, is a msu track available in the root of the game.
you have to find the point, where the game load the track und control play and stop etc. command!