Well that's a massive pain in the butt. After much plugging and unplugging of cables, I've traced a horrible 1khz whine in my audio chain to the box that connects the USB to the Mixer. These things are not repairable, so I've got to bite the bullet and replace. But that requires a choice. Get a new A/D box, or get a new mixer with USB in and out? I lean to the former, if only for flexibility, but need to do the research. After I've finished mixing tomorrow's podcast.