A: The typical way an effect unit is connected to the Aux Sends and Aux Returns is:Take a 1/4" (TS) cable and plug into one of the Aux sends output. Take the other end of the cable and plug into the input of the effect unit. If your effect device is a stereo unit, plug into the input designated for mono signals (usually the left input). Next, take two 1/4" (TS) cables and plug them into the left and right outputs of the effects unit. Take the other ends of the cables (L and R) and plug into one of the stereo Aux Returns (L and R).
With this configuration it is important to remember the different control points along the effect's signal path: Aux Send sets the amount of signal sent to the effects device. Effects device inputs set the amount that gets into the effect device. Effects device output sets the amount of processed signal sent to the Aux Return. Stereo Aux Return sets the amount of processed signal that mixes with main mix.