I tried removing the ground shield from one end of each of my signal cables and then running a good ground from the chassis of the processor to the chassis of the amplifier. The hum increased.

My next step is to replace the filter capacitors (9800uf) in one of the amplifiers and also replace the volume controls. Then I will get back to my hum problem. I want to hear one of the amplifiers with 100% of the hum gone and no volume control issues. I have the capacitors ordered and also have the volume controls ordered.

This is going to be a tough problem to fix but I know it will be worth it in the end because I really like the sound of the 9440A amplifiers.