I want to plug my macbook into my mixer, for individual volume control of the piano, bass and drums from BIAB.

Anyway to get this from my Macbook? Is there a USB/Firewire solution with multiple outs? Can I use an optical cable somehow? Will BIAB support this?

I saw this link that might have some clues:
http://forums.macnn.com/69/mac-notebooks/317398/macbook-and-5-1-surround-sound/