Changing Tubes

More air and bigger soundstage if possible 

bigger soundstage = siemens, voskhods, reflektor

More air = amperex, raytheon, french made 88, tesla, telefunken

Above are only my general observations and as  i am not familiar with your preamp you may find something that fits your requirements better.

can't go past Telefunken PCC88

Does anyone have impressions to share of the '70s/'80s Toshiba 6DJ8?

I will suggest that you first research if your pre is OK with 6dj8's VS 6922's.

If it runs the tubes (6922's) hard 6dj8's will not last as long.

If it runs the 6922's harder you will need Russian/Soviet/Eastern European 6922 equivalents and/or 7308's.

Some of the Russian tubes mentioned seem to be the currently available non EV/EB types (which are not the long life versions like the EB/EV's).

For example -  well testing/long life EB/EV versions of the Rocket/Voskhod 6922 types have not been readily available on the market for the past 5-10 years).

I agree with the Brent Jesse recommendation as he seems to have a current stock of reasonably priced Amperex 6922 types, though assume that he is swamped as of lately.

This (reasonable prices) may/will change in the very near future.

DeKay

I have been playing with tubes and found a reasonably priced good sounding tube. Sovtek 12AX7 WB. Surprised me and cheap. I compared it to PSVange and Gold Lion.