USB/Firewire/Thunderbolt connections are only between recording device and PC.
You would have the same situation.
UFX connect to PC via USB and then one or two FF800 connected via ADAT to the UFX in standalone mode.
But you would require to connect each of the FF800 to the PC as well to be able to configure or modify the routing.
You could connect two UFXII via USB, clock sync with ADAT, AES or WC and then use same ASIO buffersize.
But each unit would still have it's own instance of TM FX where it wouldnt be possible to create monitor mixes
across those instances, TM FX routing works only within one TM FX instance.
But you could route using the DAW ...
A better solution might be a combination of UFXII and Octmic XTC and to integrate the XTC as so called AUX device.
Then you can control the most important channel settings incl. Mic gain within the TM FX instance of the UFXII via MIDI.
Ideal is the combination of UFX+ and Octamic XTC via MADI, then you can use MIDI over MADI and then you have only one optical fiber cable that can even be 2km long between each of the up to 8 devices in such a MADI ring. And each of the devices is remote controllable as AUX device from this one TM FX instance.
Other advantage, also these channel settings can be stored digitally in snapshots.
This saves MIDI cabling, remote control via MIDI over MADI.
Other advantage, at higher sample rates like 96 kHz you still have 32 MADI channels, so no loss of the amount of channels by multiplexing like this is easily the case with ADAT.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14