an FX Return is just like any other channel carrying a wet signal (signal processed by an FX) In the analog world, I used to return the wet on regular faders instead of using the stereo returns if they used knobs. When on the LR mix, faders will act the way you know them. When you select another Mix (Mix1-10 or FX1-4), the faders will act like the Aux knobs on each channel strips on analog consoles. On the Qu’s top layer, Faders with blue leds, most of them represents the Aux knobs in the master section of an analog console.