QsBlues

Have you tried replacing the USB cable?

It seems too complex of a setup; why not just run everything into the mixer 1st, then into the UX2? It would make for a much cleaner signal, easier setup, easier mixing and monitoring, and you could use Logic's mastering tools to make a good recording at unity gain. If you really want more inputs, you could get a UX8 and the problem is then solved, rather than getting a Saffire Pro 40. Then, you could use the money you save on a headphone distribution amplifier, and have everyone play at the same time with more isolated signals.