1st of all it would be useful to tell which RME interface you are using and from Focusrite many different versions "* Octopre *" exist.
It would be nice to link to the device that you use to be clear on that.
Also useful: to put such info into your forum signature so that such information is there just in case you forget.

From older threads your recording interface seems to be FF400 and
I assume you have a Focusrite preamp / ad/da converter like this:

I think you have either a clocking/configuration or cabling problem.

You didn't tell which device is clock master and clock slave in your setup.

I assume the FF400 should act as clock master and the Focusrite Octopre is clock slave and gets clock from ADAT.

What you need to check (best in that order to give the troubleshooting a little bit structure):

1. In the RME driver settings ensure the following things
1.1 Set clock source = internal (clock master)
1.2 Output Format: Optical -> ADAT (send audio in ADAT format (8ch) not SPDIF (2ch))

2. Check FF400 ADAT ports and all TOSLINK cables whether they work
2.1 Take one TOSLINK cable and plug a loop (ADAT IN to ADAT OUT)
2.2 check input status whether you get a sync, then your cable is ok
2.3 repeat that for the 2nd TOSLINK cable as well

3. Clock settings on Focusrite Octopre, set to get clock from ADAT

4. Check ADAT ports on Focusrite Octopre
4.1 plug one of the working TOSLINK cables between ADAT OUT 1..8 and ADAT IN 1..8.
4.2 Focusrite Octopre: check sync status by observing green LED at the lock symbol in the middle left from level meters.

5. Proper ADAT cabling
5.1 FF400 ADAT OUT to Focusrite Octopre ADAT IN (for ports 1..8 !!!!)
5.2 Focusrite Octopre ADAT OUT (for ports 1..8 !!!!) to FF400 ADAT IN

6. Check clock status
6.1 FF400 in driver settings, do you see under Input Status: Line ADAT -> Sync ?!
6.2 Focusrite Octopre: check sync status by observing green LED at the lock symbol in the middle left from level meters.

Now FF400 is clock master and both devices are properly clock synchronized through ADAT for the transfer of 8ch in and out.

Next part is proper routing through ADAT, but this you should know after operating the device since some time ...

> I'm also using the Octopre MKii but after googling I was shocked to discover just now that somehow
> I have a version that doesn't have ADAT IN at all!

There are different variants of this device with/without WC, with/without ADAT input. That's why I also asked to specify and write the info about what devices you use in the forum signature and to make it clear for any further conversation.
But I understood from your 1st post, that your current device, that you want to connect and for what you want to have clock synch solved, is the one which has ADAT inputs and analog outputs. Whether it has WC is not so important here, as we can get the clock easily from ADAT.

> Is this a deal breaker for my connectivity?

Could we please stick to one case for now and solve one problem cleanly ? This is your current setup as you described it in your first posting, isn't it ? So lets concentrate on this as you got a solution for this so please implement it now and report back.

> However do I actually need to go RME ADAT out -> OctoPre In?

The devices need to be clock synchronized to prevent clocks drifting and thus pops/clicks no way out here.
To use ADAT is the easiest way to get the clock signal from clock master (FF400) to clock slave (preamp).
And only this way you can use the analog outputs of the preamp to expand your recording setup or how else will you send audio from the computer or the FF400 towards the preamp ?

> I guess the question is if I'm "piping out" 2 channels out of the Octopre to my pedal, the origin is the Octopre
> and the destination is my RME after the pedal grabs it, at what point of the signal flow would I send
> anything from the RME fireface to the Octopre? That's what's confusing me

The analog connections of your preamplifier do not only serve as CUE output for the recorded Signal on the preamp, but - just like the Mic/Line inputs - extend your entire recording solution with additional outputs. Either for audio from the PC with the usual latency via Firewire or in near-realtime directly from an input to an output of the FF400. How you use this afterwards is your business.

It doesn't make sense at this point to describe other scenarios here, such as you have set up something with other devices at some point. Best is to get this going and to understand how it works.

In regards to clocking .. I am not sure if you ever read your FF400 manual. You find in chapters 7.5, 30.1 and 24 valueable information to this topic:
https://archiv.rme-audio.de/download/fface400_d.pdf
https://archiv.rme-audio.de/download/fface400_e.pdf

For example that a "lock" alone is not sufficient, you need to reach "sync" status.

One short note about your other setup and the screenshot that you provided.
You said you have a Focusrite with only ADAT output.
And you operated the Focusrite as clock master (clock set to internal).

In the screenshot of the FF400 settings it's clearly visible, that you also set the FF400 as clock master and this is an absolute no go. The FF400 manual tells clearly, that in a digital setup only one device may be the clock master.

So if the Octopro is clock master (maybe because there is no other option for synchronization in cases where a certain model has no WC and also no digital inputs), then the FF400 needs to be configured as clock slave (clock source ADAT).

The settings dialog in the screenshot shows clearly that the input status of ADAT is only "lock" but not "sync".
So it shows, that FF400 is not synched to the clock master (preamp connected to the FF400 ADAT input).
Well and in such situations you may think that it works, but clicks and pops may appear because of clock drift.