I confirmation of others before me, the Furutech GTX-D NCF(R) Ultimate Nano-Crystal Rhodium-Plated AC Duplex Receptacle produced an audible difference.
In reviewing your system, I do not see power conditioning listed. I recognize your post focuses on outlet recommendations, but consider a power conditioner within your means from Shunyata or Audience. Well kept preowned is good. IMHO, more of an improvement across the board than an outlet.
Good outlet for amplifiers
I have a circuit in my listening room for my amplifiers and it uses a dedicated ground. Right now I have two duplex outlets connected - and I use the primary outlet (first on the run) for the amps (reserve secondary for subwoofers if needed). I would like to install better quality outlets for this - two duplex, set up for a dedicated ground. I could see spending $100-$200 per duplex, if that gets me something decent. I want it to grip the plugs well. Recommendations?
PS - I'm running two VAC Phi-200 amplifiers (200w tube amps, KT88)