I had your exact problem only i'm on the regular Macbook (not pro) and I don't even have firewire.

[ame="http://www.amazon.com/CyberPower-High-Speed-7-Port-USB-Hub/dp/B0006TIA8Y/ref=sr_1_5?ie=UTF8&s=electronics&qid=1284265141&sr =8-5"]I bought this USB hub[/ame]

and it worked perfectly in 20 seconds setup. I have two X1s, wireless mouse, portable hard drive, nanoKontrol plugged in and it all works fine.

Let your audio interface have its own port.