Updates:
At the UAD-1 forum it was suggested I try a DPC Latency Checker utility and I did find out that I have some moderate spiking going on which can be related to dropouts. (My old system, which had the same Lynx dropouts had no spiking.) There is a large thread on this at the Sound on Sound PC forum; many users of Gigabyte motherboards reported either earlier BIOS versions or recent beta BIOS versions reduced the DPC latency. So I emailed Gigabyte tech support and they sent me a new beta BIOS that brought the spiking way down (max of 29 microseconds). That's the good news. The bad news is that the Lynx dropout situation persists, so I don't think the DPC latency is related to my issue with Lynx, multiple UAD-1, etc.
A while back, UA suggested a PCI latency tool whereby one can set the PCI latency of various devices. This made no difference on my old system with Matrox AGP graphics. For some reason, I can't even get it to run on the new system: as soon as I try to run it the mouse and keyboard lock up requiring a reboot. Here is a reference in case it helps anyone:
UA WebZine "Support Report" June 05 | UAD-1 and Tiger plus Adjusting PCI Latency Settings to Fix Clicking and Popping Problems
I'm still trying to track this thing down ...
BTW, thanks for responding, Chris. I realize you've moved on, but I appreciate anything you have to share.