Hello,
I tried the same a couple of month ago (without much effort though) and managed to connect the Touchmix and Reaper using the QSC USB Driver for Windows. I could connect channels from the Touchmix to Reaper and record them in Reaper. I finally used only one channel at a time for sampling purposes, but I believe it would have worked simultaneously as well.
If you check out this video on QSC website
https://www.qsc.com/live-sound/produ...ixers/#c137975
(the one about 3rd party effects) you can see how to connect in- and outputs and how to do the setting in Reaper.
To be accurate, I gave up the idea of recording in Reaper before I managed to also connect the outputs of the Reaper tracks back to the Touchmix, because I didn't need it. My usual workflow is to do the multi track hard disk (SSD) recording on the Touchmix, and only after the session import the tracks into Reaper. But after watching the video I think the only step I was missing was to connect the output of each Reaper channel output to the corresponding Touchmix channel input, as shown in the clip.
If I remember correctly, you don't need to arm the channels for recording on the Touchmix, as the pre fader signals are always provided to the USB port right after A/D section, if you switch Touchmix recording mode to DAW. However, for playback, you would need to set the Touchmix channels to play mode.
Sorry, I can't double check my memory, as I cannot access my Touchmix at the moment. My reply is thus probably inaccurate and I apologize for that, hoping it helps nevertheless.
cheers Funkydrum