I am not sure whether its possible to use such a setup with two TB->FW adapters in your case.
IF it works it might block your two main TB outputs of your Apple computer.
I am not sure, whether its possible to use two TB->FW adapters in such a setup whereever you want in such a chain of TB devices, maybe behind a thunderbolt dock which might offer again multiple TB outputs.
Besides the advantage of such a solution to max out the number of useable I/O ports you should be aware of, that you have to work with two separate TM FX instances for UFX and FF800 where you can NOT route audio between the two interfaces. You would need ADAT cross connections between those interfaces to be able to route at least a few audio channels between UFX and FF800 in this setup.
So in your case with Apple M1 and UFX/FF800 it might be easier to use the UFX as main interface and clock master and to connect it through USB to your Apple. The FF800 you connect through ADAT, it will receive clock for synchronization through ADAT. Best is to use two TOSLINK cables:
Apple ---USB--- UFX (clock master) ---> ADAT --- FF800 (gets clock from ADAT IN)
<--- ADAT --- FF800
To be able to still operate the FF800 its recommended to get at least one TB->FW adapter and to install also the FW driver so that you have access to FW settings dialog and are able to change routing, the gain of mic channels, enable/disable phantom power, change ref levels of analog I/O, ..
Not sure whether you need something like this, but I want to mention it for completeness.
A more powerful, flexible, elegant solution might be to sell UFX and FF800 and to upgrade to an UFX+.
Maybe in combination with Octamic XTC and maybe even ADI-2 Pro FS R BE.
Then you have the option to connect UFX+ to your Apple through either TB, USB3 and even with USB2. Addition of Mic or Analog channels can then be performed through MADI or even ADAT.
The Octamic XTC gives you different types of channels and features:
- Integration into FM FX as Auxdevice (remote control) through MIDI over MADI
- Mic ports, that can be used as line inputs as well
- two additional phones outputs
- 4x AES I/O
The ADI-2 Pro FS R BE (which you could connect e.g. through AES or ADAT) gives you besides an excellent audio quality excellent additional features for your monitoring section (active monitors, phones) and can also act as monitor controller to have more control over the final volume not that 0dB on "Main Out" or "Phones" accidently damage active monitors or your ears.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13