Ref 2, MK 1 v. Mk, II

Do a search on the BAT preamps. I think BAT is one of the first company to jump on this tube. They probably have a lot of discussion on their website about this tube. And of course, compare to the Sovtek 6922/6DJ8s, they sound better. I suspect the redesign has to do with modifying the existing design to use this tube instead of the 6922s.

I assume we are talking about ARC Ref 2 preamp. I've heard from many that the LS-25 Mk I can sound as good as the Mk II by upgrading to NOS tubes. And it's cheaper. I am sure this is also the case for Ref 2.