Hey Kroc, I was just gonna mention that I had just this minute found Marble Zone music in the game, but you already beat me to it by 2 months. I checked throughout that music segment and found no other unused music. A great find, indeed, so congrats for that, eh?
I haven't checked out MaSS1VE yet, but I will be sure to do so and let you know if there are any problems/bugs with it. I might also see what those unknown bytes do in the game from the level headers. I'll try to help as best I can.
~ Penta Penguin ~