I just thought I would recap this topic to let anyone who may find the post know (potentially years from now, as I routinely do with topics!) that I solved it with the help of forum members and RME support.
Basically, in summary, I bought the UFX III not knowing that some USB controllers and ports are incompatible with RME gear. I had a motherboard that had a ASMedia chipset (incomatible). I bought a Allegro USB 3 card and that still didn't work correctly on that motherboard for various reasons.
Anyway, I pulled the motherboard out and totally rebuilt my computer. I have an 8th gen Intel CPU that didn't need to be replaced (i7 8700K great CPU!) so I found a compatible Intel 1151 socket motherboard on eBay that had a Intel (supported) USB 3.0 controller & chipset. I still have the Allegro card and used that in a PCI-e slot. The motherboard I chose was the Gigabyte z390 Elite which has lots of expansion slots and an Intel USB 3.0 chipset.
I can now happily report that the UFX III works completely perfectly on my system! I am so happy that this works. This interface fit my studio like a glove as far as technical digital and analog i/o requirements, which were very specific to my studio.
I have tested it for 2 days; I recorded some test tracks, listened to many records while cleaning & organizing my studio or browsing the web, and even left the system on idling for many hours while I was out and I have had zero errors reported and I have heard zero dropouts or audio glitches during that time as well.
Rock & roll baby!
Also, now I have 30 inputs and 30 outputs here on analog, MADI, and AES (the system can do 188 channels 94 in and 94 out!) on USB! I can't believe this all works so smoothly on USB. But it does. Amazing work RME.
My MADI and AES converters are working perfectly. The system is clocked via the AES ADC on BNC cables and mirrored to all the other units with one of the MADI pieces, terminating at the UFX. The clocking setup is totally solid.
Some things that I did to make sure the system stays stable: Via Device Manager, USB controllers are not allowed to disconnect or "sleep" to save power. All power management settings are maximized including the Nvidia card & drivers I have. And yes, I have an Nvidia 2080 Ultra GPU which is known to cause problems with RME gear, but it seems to be working fine and not causing any problems. I can seem to use either hte USB 3.0 Intel built in ports on my motherboard or the Allegro Sonnet USB 3.0 card, too.
Weirdly the Sonnet Allegro card method seems to take the UFX a little bit of time to be recognized, no more than 2 minutes and most of the time under 1 minute before it pops up in Windows. I asked RME support about this and they said it's normal. Once recognized the UFX is stable and can be switched on/off and is recognized again quickly. With the Intel USB 3.0 ports on the motherboard, on the other hand, the UFX is recognized in USB 3.0 mode instantly. I want to keep the UFX separated from other USB 3.0 stuff, so the choices are either to use the USB 3.0 Intel ports only for the UFX and put any other USB 3.0 stuff (drives, dongles etc.) into the Allegro card, or just put up with the slightly delayed response time of the Allegro card for the unit on startup.
Also, UFX always worked perfectly on USB 2 on my Windows machine to being with, I just wanted the USB 3.0 features because I have MADI gear. And on my Mac, USB 3.0 was always working perfectly to begin with. It was only with USB 3.0 on Windows (which is my main studio computer) that I had problems initially. Everything is now solved for USB 3.0 on Windows here.
Thank you guys! Amazing piece of gear, the UFX III. I am thrilled to own one.