NOS tube alternatives for Herron VTSP 3A r02


Looking for advice from actual Herron preamp owners who have experimented with different tubes. Recently acquired Herron  VTSP 3A r02 to be used with CAT JL5 amp. Speakers are Dynaudio C4s & ATC SCM19v2s.

I´m fully aware that manufacturer advises against tube rolling citing preamp was voiced with especially screened & selected modern tubes but I´ve decided to disregard for the following reasons:

Unit was purchased used & came with new tubes that are not originally from Herron & IM(not so humble)O & experience current production Russian and Chinese are vastly inferior in tone & timbre to NOS Telefunkens, Siemens and Amperex in relation to 6922 variants.

Thanks 


rost
I should add that for a much lower cost you could try Amperex 6DJ8s. Not as long lived but similar in terms of sound. Could call Keith to see what he thinks about 6DJ8s.
I've found that the right alternative tubes can improve an amp better than moving to the next model up. 
Any owner with info on a VTSP 3a tube position/function?

What do V1 left channel/V4 corresponding rt channel, V2 left/V5 rt, , V3 left/V6 rt channel -  subserve? Which ones need to be matched?
Does this amp need quad matching or just in pairs?