I've found the 12AT7 input tubes actually make more of a sonic difference than the 6SN7, with the 6JN6 output tubes really having very little sonic impact after trying RCAs, Sylvanias and Amperxes. I recall having tried some 5692, but it has been a number of years and I really can't remember my overall impressions. I too use RCA 6SN7GTB flat black plate with the bottom 'D' getter from the late 50's /early 60's and have always come back to these as one of the best sonic fits for all my Berning amps. The usual disclaimers apply.
-Richard
-Richard