Depends on the mixer a bit. If it’s a large one with busses or lots of auxes, I’d probably just hardwire the OT to the bus outputs or the extra auxes, so I could sample anything from the mixer by just pressing a button or turning a knob.
Small mixers (like the one I have now), can be difficult though if you have lots of units you want to sample from, and you often need to deal with plugging and unplugging audiocables a lot.