Here is the 3 secret tracks from Super Monkey Ball 2 for Gamecube I converted from the Rip (Twice), I have no idea what these we're for, but I like them, I personally like track C myself:

http://www.megaupload.com/?d=HH12TZEF

Enjoy!

I thought this music also showed up in Sonic Mega Collection where it was also unused.

You maybe right on that, but I found those in the rip and decided to convert them and see if anyone liked them or not.