Ty MC!
Took some experimenting, but I think I got every working
I kept plugging and unplugging my iPad to no avail. Turns out the key ingredient was: plug in the iPad BEFORE plugging into the UFX+.
Originally, I plugged the USB type B cable into the UFX+ first, then came out from behind my rack and plugged in the iPad. This always failed.
However, if I plug the iPad in first, then reach around and plug in the UFX+ (while TotalMix is running on iPad), it connects and I'm off the the races. A bit strange but not a huge deal.
For reference, I'm using a 3rd Generation iPad Pro w/ OS 15.7 (TotalMix 1.73)
Anyway, once I got that connected successfully, I enabled loopback on Main (AN 1/2) and then plugged the UFX+ into my linux machine. The settings persisted and I now have loopback set up. Hooray!
Regarding workflow, it seems a bit tedious to reach around the backside of my rack every time I need to change a setting like loopback in CC mode. I think what I'll do is save setups for a few different states on the device to cover my general uses, then swap directly on the UFX's screen when needed. Avoiding the iPad unless absolutely necessary.
If there's a better workflow for CC mode I'm missing let me know. (Not sure if TotalMix remote server is a compliant function of CC mode? I feel like needs a driver...I'll check the manual).
Regardless, I'm stoked that I now have a Linux setup w/ Reaper and UFX+. Doing some initial testing and it's buttery smooth.