A live setup example
If you are using AUX send 1 to feed a monitor mix you can use AUX send 2
(For example) to feed signal to an outboard FX unit. Instead of returning FX unit to AUX 2, return it to AUX 1. This will return processed sound to your AUX 1 (used for your monitors) and can be routed to L/R mix or any of the SUB Groups by pushing the assignment buttons in Stereo Aux Return section of mixer. The potentiometers in this section are for master return level, in the AUX send section next to this is the master send control for AUX busses. You will have individual send levels in each channel strip.