@gravyface ,
To combine/mix two (or more) channels a mix is required, either in the Qu or your DAW. Though of course if you are mixing them in the DAW, you’re still sending two channels from the mixer which is something you wanted to avoid.
It is not possible to send two channels/sources to one output without mixing them, and in case it helps, I personally imagine the USB channels as empty ‘slots’ which can each be assigned one thing.
That thing could be an insert send, a direct out or a mix, but the important part is that you are assigning a source to the USB channel rather than a USB channel to the source.
i.e. go into settings on the Qu and choose “USB 19” for both 19 and 20?
not possible – select the same USB channel for two sources
is possible – select the same source for two USB channels
Cheers,
Keith.