The remapping to the TRS in the back will hopefully also be available in the EX? So the ADAT 3/4 can be used with Line Levels in the back?

I was thinking about changing sample rates, though...

If sample rates change to the higher, higher numbered channels become inaktiv accordingly - like with any ADAT interfaced converter.

For my personal need it would be enough to include an expert setting which lets me choose the ADAT channel to be used at 48kHz per channel.

Also a fixed mapping would help:
Default: just as it is right now
Active:
@48kHz: fixed mapping 1/2 --> 1/2 and 3/4 --> 3/4 or something selectable (but I get that this is additional efford)
@96kHz: fixed mapping 1/2 --> 1/2 and 3/4 --> 3/4 (or if this is also a clocking nightmare: feature not available)
@192kHz: fixed mapping 1/2 --> 1/2 and 1/2 --> 3/4 (feature not available)

But of course a selection of the channel would be the nicest solution.

It gets even more complicated than what KaiS described - what happens at 96 kHz and 192 kHz where selected channels might not exist?

A minimalistic extension would be:
Make all ADAT channels 1/2 to 7/8 accessible from the source selectors.
At 96 kHz and 192 kHz all non-existing channels would be greyed out.

Everything else would stay like it is, including the clock situation.

192 kHz doesn’t make too much sense for ADAT anyway, as it’s easier handled in SPDIF format.

This change would fit to ADI-2 Pro’s and 2/4 Pro SE’s four DA channels.

This feature extension opens Pandora's box and will cause a lot of development time for a feature that 99.9% of the users never use. Plus it makes the UI and operation of the unit harder to control and understand. For these reasons there will be no such extension, sorry.

If you are concerned about "wasted" channels, why not just use the AES/SPDIF instead, as I do? Or even both of them for 1/2 and 3/4 outputs of the ADI, as you mentioned you'd like it to work. There would be no waste, and you get the same number of channels regardless of sampling rate.

I actually think the first step would be something like an additional option to select which input channel of the ADAT should be used. Or an extended list of inputs. But to keep it simple I think having an advanced option just to select the channels when ADAT is detected would be cool.
Then using multiple ADIs should be possible by using TOSLINK splitters I guess? 8 channels of audio to a splitter, channels 1/2 and 3/4 to ADI A and the rest to ADI B?

So to keep the current input channel logic I suggest of something like this:
I/O Menu --> Settings Page --> add new Menu Item (per I/O Page, Ph1/2, Ph3/4, Line ....) "ADAT Channel" with Option 1/2, 3/4, 5/6, 7/8
If Source == SPDIF optical AND ADAT is detected --> Use the selected channels from the stream.

I guess that the remaining problem will be how to handle SMUX modes?

Two (or more) ADI’s could be ADAT-daisy-changed for up to 4 stereo channels of independent outputs, or an ADI-2 Pro could be complemented with an ADI-2 DAC for 3 stereos in a simple way.
This would solve some requests that came up here in the forum over the time, including clock configuration made easy.

Thinking it to the end it’s not 100% trivial:
What happens with the ADI-2 DSP processed signal at the ADAT out?

One possibility, principally leaving everything like it is:

A channel that is selected and DSP-ed inside ADI-2 is send out processed if the option Digital Out Source – Main Out is on.
Else ADAT is just feed through.
Only, that now the option Digital Out Source – Main Out needs to be duplicated for independent 1/2 and 3/4 settings, and the source selection needs to be extended to offer ADAT pairs 1/2, 3/4, 5/6 and 7/8.

Then it would be possible to e.g. go like this:

ADAT 1/2 in –> feed through ADAT 1/2 out
ADAT 3/4 in –> DSP 1/2 –> ADAT 3/4 out (with the option to bypass DSP)
ADAT 5/6 in –> DSP 3/4 –> ADAT 1/2 out (with the option to bypass DSP)
ADAT 7/8 in –> feed through ADAT 7/8 out

In my current setup I'm using an ADI 2/4 Pro SE that gets it's audio from my UCX II via the optical input.
As far as I read the manual in ADAT mode only the first two channels are available.
For me it looks like a missed opportunity to not allow the user to select which ADAT channels to use for each of the two DACs.
I'm just guessing but I expect that RME is reusing the already proven FPGA IP for ADAT decoding so all 8 channels should be available somewhere (or less in SMUX mode of course)?

It would be amazing to just map channels 1/2 from ADAT to Phones 3/4 and channels 3/4 from ADAT to Phones 1/2 for example.

Would this be a possible addition? I know you are working on the next gen for the ADI family but this could be a cool feature (at least for me) for all ADIs.

Thanks!
Felix