I've found only slight differences between 6JN6 in any Berning amplifier application (well, in either the EA230 or the ZH270). There are subtle differences to be sure, and a cryoed tube will most likely be slightly quieter than an uncryoed tube. I've used GE, RCA, Sylvania, Amperex and Zenith, and they all perform well.
The key in the ZH270 is the driver tubes - these will have a much larger sonic impact IMO than changing the output tubes.
Mechans, I appreciate your information regarding tubes in general, but to my knowledge, there is no Russian or JAN version of the 6JN6 from the 80's, nor is there a gold-pinned iteration, nor was it ever manufactured by Siemans or Telefunken, nor was there a black-glass Tung Sol. As a horizontal output amplifer (Compactron) for TV sets, this tube pretty much ceased production in the mid-70's, and being an American invention, I am not aware of many foreign sources for this tube.
Good listening,
-Richard