The mixer would be a better choice - I don't see any reason that it needs to be USB though unless for recording purposes ?
So here are the pros and cons to those two pieces of equipment which you should really look at;
Akai EIE Pro;
Pros: On paper it looks to provide better fidelity than the Xenyx
Cons: Any channel processing will have to be done by the computer and "may" add latency to your overall setup
Pros: Will handle channel EQ'ing and some basic compression withouth the need of a computer
Cons: On paper it does not offer the same fidelity as the EIE Pro
So with all of that out of the way I would suggest you ask yourself this. Do you need to do any EQ'ing or processing on any of your other gear? If not the EIE pro will offer you better fidelity according to the white papers. Otherwise the Xenyx can work as well.