Hey guys.. trying to set up a HX effects unit through through the effects loop on a Phaez duophonic guitar head. Hooked up.. send from amp going to left mon input and left mono output going to return of the amp. Works fine like this but with a cable going from my channel switch jack to the ext amp 1 jack on the board the channel switching will not work. If I remove the send and return cables the HX unit switches channels no problem. Any ideas on why this is happening?