If you enjoy the original retro electronica soundtrack used in Super Grav, created especially for the game by DaveDexterMusic, then why not check out the digital album, available now for your listening pleasure:
Super Grav OST by DaveDexterMusic
It's "name your price" with no minimum, but all donations are greatly appreciated.
Note: The music in the secret bonus game is me on keyboard playing Beethoven's Für Elise