Well, finally got the Emotiva CMX, but the hum is exactly the same. Nothing I've tried has made any difference. So, it's back to Coincident in Canada for service. Hopefully, they'll be able to diagnose the issue quickly and get it back to me relatively soon. Shipping took three weeks to get here (Oregon), so at that rate it will probably be a couple of months before I get the unit back. I guess I'll just pretend that I like my solid state amp in the meantime :)
Thanks to everyone for your suggestions. I'll let you know when I get it back and how it works out.
Best, Scott