Easy

Connect UC to UFX via ADAT.
I would use 2 pair of ADAT cables for both ways because you also need clocking information from UFX.
UC -> ADAT OUT -> ADAT CABLE   -> ADAT 1 or 2 IN -> UFX
UC <- ADAT IN    <- ADAT CABLE2 <- ADAT 1 or 2 OUT <- UFX
Connect UC also via USB so that you can configure it.
In Driver settins dialog configure for the UC to get clock from ADAT.
For the UFX set it to internal clock.
Assumed the UFX is your main interface on PC.

On UC:
- route Mic 1+2 through ADAT channel 1 and 2
- and if you want route also 6 Line INs of your choice  through ADAT channel 3..8

Either you keep both devices connected, so that you can control both interfaces with an TM FX instance of its own.
In detail: you open a 2nd instance and select the UFX and UC on the upper right side.

Or .. you configure the UC once, store the setting for standalone operation (you have to read the details in the manual),
I dont remember now exactly. And then once its done you disconnect the USB connection to your PC.
Now you only have connected the UC via 2x ADAT to your UFX and get clocking from there.