You can use my Excel to compare between UC and UCX (and other USB / FW / TB interfaces): https://www.tonstudio-forum.de/blog/ind … B-MADIfac/

Direct link to Excel: https://www.tonstudio-forum.de/index.ph … 0-08-xlsx/

Other differences between UCX and UC (besides FX and Autoset):
- lower converter latency [samples] and the sum of AD/DA in [ms] (at 44.1 kHz):
               UCX:  14     /  7 (0,32+0,16=0,48ms)
               UC:    43,2 / 28 (0,98+0,63=1,61ms)
- Preamp technology of Micstasy/UFX
- Class compliant mode (Linux, iPAD)
- Stand alone operation: 6 standalone profiles vs last settings

The slower converter latency is not disturbing for normal use cases like e.g. recording or direct monitoring of vocals through phones. Maybe only if you add several external devices through individual analog ports, then you have for each of the devices the RTL (including higher converter latency).

I wouldn't choose apollo or motu for several reasons.
Apollo: you pay for the money and the shark CPUs / the ability to run expensive plugins on the box, but the shark CPU power is relatively low, so depending on what you want to do, you can quickly need more CPU power and this is expensive.
By throwing in much money for such a solution (where you do not need the plugins on recording interface side you said) you pay a lot and are bound to that platform. IMHO Feature wise it doesn't come close to a RME solution with TM FX, TM Remote, DIGIcheck.
Audient .. well .. once you had RME I would have doubts that you want to leave RME with TM FX (and its quality and flexibility).
Another thing is driver stability / low latency / high reliabiliy ... All flashable via FPGA, etc ..
The RME concept of devices and its drivers / software including SteadyClock is much more advanced and carefully designed.