OK, according to what your pictures show you actually have a one piece system with a TT and receiver in one chassis. It would seem you may have a problem with one channel of your gear. You could try cleaning all the switches and controls with Caig De-Oxit.
ARC SP9, HW19, RB300, Sumiko Blackbird: Front: Magnepan 1.7, 2 x 12" TL subs 2 bridged Crown XLS 402, 2 modified Dyna MK-III's. DBX-223XS, Behringer DSP1124P, rear: Acoustat Model 1/SPW-1, Behringer CX-2310, 2 Adcom GFA-545