I'm interested in doing some solo recordings with my iMac G5 and garageband2. It would be simultaneous vocal and guitar. I have a couple mics and a mixer board that can output upto four channels. I've used RCA -> 1/8 inch cables into the computer before and found the sound quality to be not great. So being in the market for an audio interface, would it be better to get a cheap RCA -> USB or another one like the M-audio fastrack usb. In garage band will it let you input two simultaneous channels? If I wanted to do overdubs (one or two) would one help avoid any latency issues? If you monitor from the usb interface is the sound sync'd up better? Thanks!