You can not access both units by one RME ASIO driver, as they use different drivers.
The Digiface USB does not support stand-alone operation, so you need to take the Digiface USB as primary interface.
You have to connect the UCX to the Digiface USB with 2 TOSLINK cables:
- towards UCX for sending audio for D/A and to transmit clock signal
- from UCX to receive audio A/D
Clock master is Digiface USB (clock source: internal), Clock Slave is UCX (clock source: ADAT).
UCX: for stand-alone operation you can load setup from 6 user and 2 factory setups.
To prepare routing for stand-alone operation you connect also the UCX by either USB or Firewire.
USB allows you to perform firmware updates as well.
If the configuration of routing has been done for the UCX then store configuration in one of the 6 user profiles.
Then you can disconnect the UCX.
How TM FX works with 2 audio interfaces.
In the upper right corner of TM FX window you have a selection box to select either UCX or Digiface USB.
Whats also possible to open a new TM FX window and to have one TM FX window for each of the recording interfaces.
If you save this to a workplace file on PC or by using the Quick Workplace Select feature then even the window placement
of the two different TM FX instances are being restored.
See manual for details what is being stored to snapshots and workplaces.
I recommend to store snapshots and workplaces to the PC into files.
Then you can recover all settings from these 2 files on every PC (if you restore from backup or copy these files to other PC).
After you have done this I suggest to use also the Quick Workspace Select feature, as then you can recall up to 30 different configuration additionally and recall setup 1..9 with ALT-1, ALT-2 ...
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13