I too did an outlet shootout test using a 4 gang box , used a Medical grade double cryo'd , a lower grade Pangea , a P.S. Audio and an Audioquest NGR Edison , plugging in the amp only .
I had the opposite experience than you , each had an effect on what I was hearing with the Audioquest sounding the best .
I would love to have tried a Furutech or Oyaide but they are $100 more than a Audioquest .