The insert points on the Qu only allow the internal FX to be patched in.
To use an outboard FX unit as an insert on the main mix, you’d have to run from the main output to the FX unit’s input, fx unit’s output back into a spare pair of channels on the Qu, DON’T assign those spare channels to LR, but instead assign them to a spare stereo mixbus, then feed the PA from that mixbus.
Using outboard as inserts on a channel is a similar story: Un-assign channel from LR, route channel to mix (post preamp,) mix out to fx, fx back to spare channel, treat this spare channel as the wet channel.