@smilindan
In the CQ, select the channel where you want to hear the return audio in the processing screen.
The CQ includes a dedicated stereo USB channel for exactly this kind of application, so I’d recommend using that!
Make sure the channel is in Complete mode – if not, you can either convert it from the drop down menu at the top right, or use the library to recall a Complete channel.
Select the preamp section at the top of the channel.
You’ll see the source of the channel listed and be able to switch to the USB/SD source if needed.
In Reaper, remove or disable the main output hardware send (by default 1&2).
Add a new hardware send to the channel number/s listed on the preamp screen in the CQ.
Done!
This can be applied more generally too, i.e. repeat for every channel if wanting to send multitrack from Reaper to the CQ.
The thing to maybe watch out for when using multitrack is to turn off the parent send from each channel in Reaper, otherwise you’ll end up with the individual channels and the main mix being sent to CQ channels at the same time.
Hope this helps,
Keith.