Yes, I'm back in business. Thanks again.
I was 99% sure it was going to work when I checked it today and it did. For some reason, I thought I might have to pick DLNA on the mRendu software, but of course I did not have to as I had done that last night (proven empirically by the Zone showing up again).
When you said "just leave the Roon Ready operating mode entirely", I finally saw what you were talking about. I had seen that the various icons when working with Sonore tech support, but don't recall ever clicking/selecting it to get Roon to work. Similarly, I am almost certain that I never selected the DLNA/UPnP endpoint icon to get the mRendu to work initially. My original mRendu worked for about 18 months before failing and me eventually having to get it replaced.
As far as looking for the device to "show" (be recognized) on my OS, I reasoned that if the computer did not identify the device, JRiver would not either. I just checked my Win 10 machine and on File Manager and under Network it has "mrendu0286-media server" showing. It has a new icon that looks like a penguin with headphones. Definitely not seen that until tonight, but it had some kind of icon before. On the Mac (which I am currently on), when I go to Network, it says "MRENDU0286EA." So just trying to explain what I was looking for.
I know enough to be dangerous, but sometimes miss obvious stuff. I had rebooted (and Shut Down) the mrendu several times via Sonicorbiter, but didn't even really know that the mrendu was considered DLNA. I thought that was different topology for some reason.
So, once again, thanks for everything!