I think I will wire two of the four plugs that I have dedicated to my setup, and try just two through the transformer. Then I would have the option of trying both ways. If I like what I hear I will probably wire the others through the transformer.
I do not have any ground loops. My preamp and phono have ground lifting switches so I have those configured so I get zero hum as far as loops are concerned. I had a separate ground plate installed and ground isolating plugs wired, but I found zero benefit doing that. I may use that ground plate and have the new breaker box grounded to that. The main breaker box is grounded to a cold water pipe. I also only have a 100 AMP service. Too many large and small factories around that I assume would affect my power in my area.
The main thing I want to address is the physical hum I am getting from my amp. The power transformer hums, depending when I listen during the week it is very annoying walking into a quiet listening room and hearing that transformer humming. I know the amp was quiet at the dealers room. The builder of my amp says I have DC polluting my power, I borrowed an item from Blue Circle http://www.bluecircle.com/page129.html and it was very effective. It did what it was supposed to do, but I felt the it was a sonic compromise I was not willing to accept.
Paul
Any transformer will have a sonic penalty, you're not going to get away from that. I have to agree with with TP1, your amp designer has a responsibility here. I don't know thei brand he used but they could be low in quality or defective, it happens even with the best transformers and often manufacturers are either adamant to reject them or sometimes the defect shows up later.
david