The QU16 does not have audio groups.
With that I would use a mix, set it to post fade and post processing.
Set all the needed mic channels mix sends to the same level.
Set the mix out to send via USB to the DAW on the track the DAW wants to see.
You may not need the mic channels to be the main LR mix, if not un-assign them
from the main mix.
Un-assigned or not you can sill use the main mix layer to control the levels with the
mix set to post fade.
As a bonus the Qu mixers have an auto mic mix function, perfect for what your
doing, go to the set up menu, select the audio tab, select AMM turn it on and select
the mic channels your using, select the set up button on the AMM and then turn on the
follow fader option.