Not sure how flexible you are in terms of budget.

The best option IMHO would be to get the UFX II without compromises, as you get then best quality paired with most flexibility
- Latest converter technology with lowest latencies
- new analog circuit design compared to the old flagship interface UFX, best sound
- Durec allows connection of USB stick or harddisk to be able to record either fully stand-alone without PC
or to have a backup running in parallel to survive a potentially hanging PC during a recording session,
shall you make recordings of your life shows
- improved phones outputs
- display allows for fully stand-alone operation in addition to 6 recall-able user presets
- Class Compliance mode allows i.e. connection of iPAD to run either TotalMix FX and / or Cubasis
- FX chip on board
- possibility to connect ARC USB directly to the device
- a powerful 30 channel IN / 30 channel OUT recording interface, which doesnt put any high requirement
on the computer hardware, as 30 channels IN and OUT can easily being transferred via USB2 still.
So you get most flexibilty and do not necessarily require USB3 ...

You can read some additional information in this blog article that I wrote.
The UFX II is same as UFX+ (minus MADI, minus USB3, minus Thunderbolt).
https://www.tonstudio-forum.de/blog/ind … 8-RME-UFX/

There you also find an screenshot of an Excel comparing the RTT times which the ASIO driver reports to the DAW.
UFX, UFX in front of a RayDAT, UFX+ .. all nicely compared.

Then maybe also have a look at the UCX. You can use also my comparison sheet here:
https://www.tonstudio-forum.de/index.ph … 17-12-pdf/

The UCX came out 3y later than the UC, it has quicker AD/DA converter built-in. There are also other differencies, which could be worth for you to consider, maybe spending €300 more .. Especially as the UCX supports Class Compliant mode which could be very interesting for you from performer perspective.
Now 1st the device differencies, later some more info on CC-mode:

• USB2+FW400 (2 options)

• Newer converter with lower AD/DA conversion latency [samples]: 14/7 vs 43/28 (UC)

• Micstasy/UFX preamp technology

• Has AutoSet which is very useful to find proper gain settings quicker. UC has no AutoSet.

• Complete FX chip on board (Reverbs, Delays, Dynamics), UC has no FX chip

• UCX is fully Class Compliant, UC only MIDI

• Stand-alone capabilities: UCX has 6 different stand-alone profiles which are recallable on the device, UC: last settings.

Class Compliant mode enables you to connect i.e. an iPAD with TotalMix FX or Cubasis running on the iPAD to enable for such a PC-less setup, as shown on Messe Frankfurt:
https://www.youtube.com/watch?v=YjyIBKR798c
https://www.youtube.com/watch?v=msD2fnAEwec

I think from a performer perspective this would give you an additional value for just right now and the future.

Because it has not AD/DA converter. Its a pure digital interface with only a monitor output for phones.

If you plan to connect your audient to the digiface via ADAT then you need to consider the AD/DA latency of the Audient.
Inside of the digiface usb's routing matrix you will have near zero latency.

If you use effects of your DAW you need to add the Round Trip time between Digiface USB and your DAW.

Another thing to consider, I am not sure whether your audient can be used in standalone mode.
Eventually you have to connect it as well to the PC so that it gets proper initialization.

Easier would be to work with one device.

You can take the UC, but I still would recommend to spend a few bucks more for the UCX for the named reasons.
You can take also the Digiface USB, but then you have to work with 2 recording interfaces which increases a little bit the complexity of the setup.