What you want is a firewire or USB audio interface, or an audio interface that connects via the express card slot on your MBP. There are literally hundreds of these devices on the market, so peruse the various on-line retailers. However, you may be better off with something like a Microtrack or R-09 or something similar, especially if you're going to be recording 2-channels and not multitracking. You'll spend less money and won't have to take your MBP into a venue.