Bill I thought I'd update you and anyone else watching this. I have spent hours on 3 different levels of Microsoft support. They are all stumped. The last option suggested was blowing up the machine and doing a cold re install of Windows 10. I'm not willing to do that right now, at least not until tax season has passed!
The last guy gave me another number which seems to be the standard Microsoft 365 number. Not much hope there.
I have one other thing I might try. Uninstall all sound drivers and remove the devices, then do a repair upgrade (which doesn't lose programs) with no sound devices. May remove the serial devices also as they are also affected (they show up, but they don't work). Again, all other programs do this ok, including MIXW4, which this has forced me to get used to!
I'm completely willing to do any tests you might have, and I would love to hear any ideas you might have on this issue. This is definitely the strangest Windows problem I've ever had, and I've been at this stuff for over 30 years!