You could always buy some 1/8" stereo single to dual 1/4" plugs and run them from the stereo output jack into an inexpensive mixer (run the monitor mix direct from the board), or you could just get an inexpensive firewire or USB interface and have better sound quality and multichannel availability. As for the PB performance, I'm curious as well...thinking of getting one for portable Pro Tools setup (DIGI 002 rack). Let me know if you find out! Seriously though, you should get a dedicated audio interface...the Mac soundcards are pretty decent but not sufficient for quality audio work. If you're not looking to spend a lot of cash, look at the Digidesign Mbox (400 bills). Pretty nice little unit (for the money). If you are flush with green...DIGI 002 rack is kick ass. Same as the MOtu gear (with Digital Performer software). Tascam USB interface is not bad either. Good luck...