The Qu range of Allen & Heath mixers do not have dedicated send and returns for external hardware.
As a workaround you can do the following:
- Send audio from your DAW to Qu's input channel/s.
- Send audio from the input channel above to a Mix Output (Mix 1, 2, 3, 4, 5-6 etc).
- Connect the Mix Output to the input/s of your outboard gear.
- Connect the return from your processor to a new input channel/s on Qu.