In general RME USB driver deliver a performance which is very close to PCIe.
Its more the point how well your PC performs and is set up for audio.

Differences of these interfaces

The Digiface USB has a phones output and all four ADAT ports can be switched to optical SPDIF.

The RayDAT is a pure digital card, the 4th ADAT port is switchable to optical SPDIF
and it gives you by breakout cable additionally
- 2x MIDI I/O
- 1x AES I/O and
- 1 coaxial SPDIF port
For the RayDAT you can get an optional daughter card to support word clock if needed.

In terms of the 2 MIDI I/O of the RayDAT: this has the advantage to have separate MIDI ports for instruments and to remote control other RME equipment via MIDI by a dedicated port.

About the ADI-2 Pro

The ADI-2 Pro can be connected by AES, ADAT, optical SPDIF, coaxial SPDIF.

The ADI-2 Pro does many things automatic, i.e. muting monitors when you plug in phones.
If you want to keep phones connected then you want to make routing to phones or monitors switchable.

Especially the RayDAT offers to you two possibilities:
1. switching between monitors and phones by routing audio to either ADI-2 Pro's AES or ADAT port and
then using routing inside of the ADI-2 Pro
2. by using the mappable keys on the ADI-2 Pro
3. or both

to 1: with the RayDAT you can connect the ADI-2 Pro by AES and ADAT.
The ADI-2 Pro can be configured to route AES input to monitors and ADAT input to phones or vice versa as you like.
With this setup you only need to provide 2 different routings in two different Snapshots of the RayDAT
and by this you can control switching between Monitors and Phones by TotalMix FX Snapshots.
ARC USB integration: This way its even possible to control this by using the ARC USB to select the TM FX snapshot to route audio to either monitors or phones.

to 2: In contrast to that its also fine to use the remap key feature of the ADI-2 Pro to switch between monitors and phones by pusing a front knob.

to 3: you can also combine both .. whatevery you want / like, this environment gives you the flexibility.

See also these two blog articles that I wrote to these two topics, its explained there in detail:
https://www.tonstudio-forum.de/blog/ind … ort-DE-EN/
https://www.tonstudio-forum.de/blog/ind … our-Setup/

I would go for the RayDAT if mobility is not required, because it offers you greater flexibility
- more ports / different types incl WC option
- more options to make best use of ADI-2 Pro in combination with ARC USB
- "ideally" connected via PCIe (*)

(*) Although nowadays there is (at least in the RME universe) no big or noticeable difference between USB and PCIe.
If you have a modern machine, which is designed for your typical workloads and if the setup and components are well,
then there is no difference, at least I could not see any difference on my PC.

See also my UFX+ stresstest of 400 tracks and ~800 VST plugins @44.1 and 96kHz and minimum ASIO buffersize of 32
https://www.tonstudio-forum.de/blog/ind … cks-de-en/

In terms of latency, see the Excel in this blog article which compares the RTT between different RME solutions which I own.
https://www.tonstudio-forum.de/blog/ind … 8-RME-UFX/