Tube rolling question for VK75 SE owners

I am looking for any feedback, recommendations, suggestions and experience
from owners of BAT VK75 SE regarding tube rolling (6SN7 & 6V6GT).
What sound best, make this wonderful amplifier even better or create
best synergy with this amp? Any problems with NOS tubes?
Did anyone tried Brimar CV1988?
Please, let me know. Your help is very appreciated.

Thanks, Jack.
hmm those 6sn7's are important. I just had one go bad. Put a sovtek in as a temp until a new russian one comes in from bat. I can hear a diff inf the channels. It's slight, but there.

I'm curious on this one now...
What kind of difference?
Is it for better or worst?
I am thinking about replacing Sovteks with RCA, Brimar or
Sylvanias. Wondering about potential sound improvement.
You might try the STC Brimar CV 1988. Some call it a Mullard.I use this in place of the 6SN7 tube in my Audio Note amps and the difference was huge. Much better detail and midrange clarity. Bass takes about 100 hours to fully flesh out. So be patient.
I have a VK-60 with Raytheon 6SN7 and they sound VERY nice. Might work in a 75SE as well.