Ensure you are in TM FX "Submix mode" (upper right box)
Perform for every HW output channel in the bottom row (which is also called a "submix")
1. click to the particular HW output (bottom row)
2. turn down (and/or mute) the fader of all HW inputs (top row)
HW inputs are always send to the Application (DAW), so therefore it doesnt block anything in terms of sound if you perform point #2.
At the end its best to store this setting to one of the 8 TM FX snapshot places (right side).
Look at my TM primer and RME tutorial video for more information about settings and routings and how to store your config.
https://www.tonstudio-forum.de/blog/ind … rnal-equi/
https://www.tonstudio-forum.de/blog/ind … al-Videos/
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14