I just realized that I ask you a question about your tube type and then failed to respond.
I agree with Autospec about Amperex 6922 Holland, not because Audio Research does not approve, but rather the way they perform in that piece.
If you run Amperex it should be the 7308 US military spec tube, preferability the CEP. This tube is extremely linear, has good microphonic characteristics and has a transparent but neutral tonal balance.
For a warmer sound the Mullard 6922 gold pin works well, and even the Siemens Cca might be worth a try, although it may prove too bright in that piece.
Unfortunately the Sovtek 6922 is not a very good tube. If it were brought in line with their 12AX7 LP, it would provide much relief for the scarce market of 6922, 6DJ8, and 7308 type tubes.