Yes the FD-4 has 1/4inch inserts for channels 3 and 4.I guess I'm supposed to mix everything over to channels 3 and 4,then do the final mix from there.Ok tell me if I'm right.I plug the stereo ends of the Y cables into inserts 3 and 4.Then the other four plugs go to the input/outputs on both sides of the compressor.Whats AUX RTN2 used for?