Thanks for the flowers. Well, I am the opinion that one recording interface has always advantages over using two.
Especially the UFX III is the most feature-rich, compact and the basis for a more versatile setup in one unit.
You are more flexible in creating monitor mixes as everything can be routed through the internal matrix with only the converter latency. With two devices makes routing more challenging and cumbersome. In some scenarios you will have to route channels between the two different recording interfaces through the DAW with the full RTL. The one digital ADAT I/O of the UCX II supporting only 8ch at single speed won't help much.
Another (IMHO) disadvantage is, that with the 802 FS you do not have the possibility to digitally save and restore all channel settings (mic channels and phones).
Furthermore, in cases if you want to use stand-alone features, you will only have it more tricky when having to operate two units separately. Especially if you should need to operate / change routing on the display.
Finally, you are with MADI much more flexible. Number of channels / devices allows for more grows. Much more possibilities to distribute devices across rooms using multimode fiber. More spare channels in TotalMix FX for special routings, monitor mixes and mixes for loopback recordings. You can add converters with higher number of ports and having the same type of converter with the same converter latency over ADAT, MADI.
When using e.g. 12Mic (which has no MIDI port) you will need MIDI over MADI (which you only get with MADI) to remote control the unit via Auxdevice support. Workaround is to use RME connector in combination with LAN connection, but this can be more tricky in life scenarios compared to the possibility to use MADI are multicore and to run remote control over it.
Based on my experience and running a quite flexible setup with a lot of functionality, I would always recommend UFX III instead of a combination of multiple interfaces to be open and more flexible for new demands.
Maybe for your application this is sufficient, but I still could imagine, that working with one unit and having the flexibility of MADI brings more features and value for you in the long run.
If, then I would sell the other units to cross finance just right now when they are new. Chances are high of reaching prices in the range of 75-80% of street price.
Just my $0.02 on this topic, your mileage may vary.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14