Hi MC,
I've owned the RME Babyface Pro for some time, and hooked up some gear to the optical SPDIF port.
I've got two digital microphones the Neumann KMS104 D and KMS 105 D using the AES42 interface standard hooked up to the Neuman DMI 2 portable. From there I passed the AES 42 out signal to a Hosa converter box Model: ODL-312 Optical-AES/EBU link using the optical Toslink/SPDIF patch cable into the SPDIF port on the RME Babyface Pro.
tech spec on mics KMS 104D, KMS 105D
Max. SPL: 159 dB, S/N: Ratio 78 dB, Sensitivity: 4.5 mV/Pa
This is how to get digital microphones to work with the RME Babyface Pro! 
Fortunately, Neumann wrote their RCS software in 2019, so it is fairly recent. Driver version for the DMI-2 portable v2.8.30.0 date:2013-07-12 provider: FTDI and digitally signed by Neumann.
Using Windows11 v22H2 build 22621.755 and RME driver v 1.2.22.0 I can successfully use the external clock function and use the digitally controlled microphones via the clock mode in Fireface USB settings setting clock mode to "optical". The sample rates 44100Hz to 96000Hz work without issue. Mics show up on hardware inputs AS 1/2 and hardware outputs AN 1/2 in TotalMix. When I set the clock mode optical to 192000Hz I get a little crackling in NDH-20 headphone output of the BabyfacePro channel Ph3/4.
I read a little further in the Neumann manual where they state:
"AES/EBU OUT
3-pin XLR connector for the AES/EBU output signal.
The AES/EBU signal includes 2 standard audio channels.
The audio data of two mono microphones are distributed to the left (CH1) and right (CH2) audio
channels of the AES/EBU output signal.
A digital stereo microphone is supported at AES42
microphone input CH1 only. In this case the audio
data of the microphones are routed to the left and
right channels of the AES/EBU output."
What am I missing when the channel width is halved...?
Should I have only one mic on channel 1 of the DMI-2 when shifting to optical clock of 192kHz with the SPDIF toslink to the BabyfacePro to achieve optical clock sync?
Superlative digital mics are not dead, they are just resting...for a little more technical info.
Ah HA...I know splurge and get the RME DMC842...!

Am I on the right track here...? pun intended 
Cheers
Hans
edit: Okay I'll answer my own question...
Powered down computer, DMI-2 and RME Babyface Pro respectively, removed one of the mics, rebooted. RCS software wouldn't pick up the single mic.
Repeated procedure, reconnected mic, and DMI-2 picked up both mics.
I was able to select 192K on both the DMI-2 and the Babyface Pro interfaces respectively.
Result: Optical Toslink/SPDIF connection now works with both mics running through the Hosa AES42/EBU converter linking to Neumann DMI-2 at 192KHz with optical clock mode in "Sync" via the RME Babyface Pro.
Snap, crackle and pop is gone...
All smiles

Cheers
Hans