Do you mean MADIface USB?

This doesn't bring you further. The device doesn't support Word Clock.
For clock synchronization, you would need to connect it to a MADI bus of the MADIface XT.
And if you do this, you do not get any additional MADI bus more.

What about using a MADI media converter like this one?
https://www.sonible.com/mlmio/

The HDSPe MADI FX could be an option, the 3rd MADI bus can be replaced by an optical module (OPTO-X).

Alternatives (maybe a little over the tops in terms of add-on costs, I only want to mention it):
- old MADI bridge (from used market): https://archiv.rme-audio.de/en/products/madi_bridge.php
- MADI converter: https://www.rme-audio.de/madi-converter.html
- MADI router https://www.rme-audio.de/de_madi-router.html

EDIT: Another idea. I am uncertain whether it's possible, check manual or ask RME.

To be checked: whether the MADIface USB can get clock through MADIface XT's BNC connector, but to use it's optical port

  PC
[USB]
|  |
|  + MADIface XT    --- MADI Bus 1 optical---devices
|     (clock master)  --- MADI Bus 2 optical---devices
|                             --- MADI Bus 3 coaxial
|                                       |
|                                    (only for clock synch)
|                                       |
+ MADIface USB --- MADI Bus Coax
                          --- MADI Bus optical-----devices

Then you could route between the two TM FX instances at least through the application / DAW.
You need to ensure, in driver settings manually, to use the same ASIO buffer size for both devices, or you get an offset.