It is a big circuit and I can understand how difficult might be to change the connections.

But in most cases that involve audio amps or pre-amps, the problem arises from the ground loops. And I see a lot on your photo Art.

So, I would suggest to take cables from all the minus (ground points) of the circuit parts and connect them to a single point where your (-) of the power supply is.

This wll also help you reduce the spikes on your digital power rail.

I suppose that you are having different power line for the analog and digital parts, right?

Ioannis