Hi Eric.
You should make yourself familiar with TM FX basic operation.
See my intro here https://forum.rme-audio.de/viewtopic.php?id=34394
Thanks for providing the screenshot, it makes the issue clear.
1. enable submix mode, you are in free routing mode
2. select the HW output (aka "submix") for which you want to configure the routing
You will see then at the bottom of each fader the name of the selected submix/HW output
3. Simply move the fader of HW inputs and SW playbacks (audio from PC) to create the submix
One of the best things about TM FX is, that each HW output has its own submix.
Like with a normal mixer, but before moving faders, you need to select the submix. OK?
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14