@travisg Sure, I replaced the 6C45 with the Russian Reflektor 6C45, more detail and clarity. I replaced my 6922 with Siemens E188CC/7308's and the result is extreme clarity, dynamics and transparency. I have the Sophia Electric Aqua 274B Rectifier Tube in the power supply which added better instrument separation cleaner tighter low end.
From Dan on the AudioCircle Site......We provide JJ ECC88's (equivalent to 6922, 7308, 6dj8). Considering ECC88 (Euro designation), 6dj8, 7dj8, 6922 and 7308 to be equivalent and all work in the unit:
Telefunken: VERY Detailed and fast sounding!
Siemens: Also very detailed and resolving.
Amperex: Resolving and very balanced.
Brimar or Mullard: British sound, a bit more warm and relaxed.
There are many more, but these are the ones that I have experience with and that pretty much cover the tonal spectrum.
Hope this helps and I'm sure you will hear the differences in your awesome system. It is hard to believe that the move from the Parasound is a lateral one, that said maybe some NOS tubes might make a difference.