I personally have never found any good USB audio device the smaller bandwidth because of USB redundancy is not much good for audio use. Do as everyone has suggested and go with a Firewire device. I like the Tascam FW-1884 because it has active faders and 8 ins and 8 outs. There also is a model with 8 ins and 2 outs FW-1080. But I've also heard really good stuff about Apogee Duet which would probably be all you need.
Take Care,
Kylee
Take Care,
Kylee