Well, it is a little hard work to read the manual chapter 6.2 of the cards and combine the whole thing in such a way that all cards are synchronized
One thing in advance, the oldest card unfortunately has no internal X400/X401 connectors, otherwise you could have synchronized all cards internally by word clock (via a 3-wire cable).
Buying the separately available word clock module for all cards would be a pragmatic solution and would not take up any SPDIF port, but would be the most expensive option and would then also cost 3x€109: https://www.thomann.de/de/rme_wcm_hdsp_9632.htm
Cabling option 1, fully internal:
One possibility I see is to make the AIO Pro FS (with FS clock) the clock master and synchronize it via the internal WC ports X401 and X400.
And from the RayDAT with X502 (SPDIF OUT) to the 9632 (SYNC IN). This seems to have taken the external SPDIF Cinch connector for this purpose, but no matter, you have enough digital interfaces with these three cards.
The manual gives hints on what to configure in the Settings dialog.
Cabling option 2, 1x internal, 1x WC
Internal WC cabling between AIO Pro FS and RayDAT via X401/X400 internal plugs.
Buy 2x WC module for 9632 and RayDAT.
Then external WC cabling between RayDAT and 9632. Read comments in the manual, then this doesn't impact the exernal Cinch connections for SPDIF on the 9632 ... you need to read that stuff and come to your own clue.
In this case added costs and you need external WC cabling and additional 2 Slots free in your computer, not with a PCI/PCIe socket, but space must be there to mount it.
- all cards use the same ASIO driver, i.e. the DAW can access all cards.
- all cards must be synchronized (however), I would make the card with FS clock (AIO Pro) the clock master.
- all cards must have the same ASIO buffer size set in the Settings dialog
- you have to work with three different TotalMix FX instances, either you change the card in TM FX or open a window for each card
- you can't route audio between the cards/TM instances
- If you still want to route between the cards, you can only do it in the DAW
That's why I probably would have gotten something like a UFX+ for simplicity's sake, where you have a lot of ports with one card, or HDSPe MADI FX (which even has an FX chip on board).
You can take the ADI-2 FS, the digital port is AES compatibel, but needs an adapter card, see manual ch 6.6. Then you could connect it via AES to e.g. RayDAT which has an AES output.
I would maybe consider to take an ADI-2 Pro FS R BE because of the advanced features and quality and connect it directly via AES to the RayDAT with a normal AES cable, if the ADAT ports are all needed for other things. Alternatively you could connect it via optical SPDIF or coaxial SPDIF, I would prefer optical SPDIF or AES because of the galvanic isolation.
I hope I didn't overlook something, this is a little bit "fiddly" topic.
X10SRi-F, E5-1650v4, Win10Pro21H1, Cub11Pro, UFX+, XTC, 12Mic, ADI-2 Pro FS R BE, RayDAT