Funny enough, I put that list together precisely so I could remember what I've had!
I have been mainly using NOS tubes all these years but I think I am going to embark on an experiment to see what good I can get out of new-production tubes. I want to try those Tung-Sol 12AX7 Gold pins. 12AX7s are the only tubes in common between your amp and mine. Anyway, I bet new stock tubes aren't as bad as everyone likes to make them sound, and besides, they are cheap enough to be guaranteed high value at a minimum. We'll see.
Have you tried running your amp in "Twin Amp" mode? I think the MkIV still has this feature. This gives you access to the gain controls. I recommend you at least try it with the gain controls turned up to 2:30 or so. I feel that really improves imaging and definition over the regular "stereo" inputs. At least it more than makes up for whatever deleterious effects the pots might cause the signal inherently.
I say "Ouch!" for your ARC monoblocks! haha. Well sometimes that is the way it goes. It is all about synergy afterall.
I also have Boltz CD racks and like them a lot. I actually need to buy another one soon - my 2 CD330 and CD600 are totally full!
Enjoy the music
Arthur