For those with Ref 2 Mk II's who aren't quite ready to trade up yet, here's a suggestion.
I recently swapped out the stock 5AR4 tube in my Ref 2 Mk II for a Gold Lion, and I was blown away by the changes. It added a kind of "immediacy" to the sound that wasn't quite there before, made it much more involving, almost seductive, like you had to tear yourself away from the music. Gold Lions are hard to find, but other NOS tubes may produce similar results. I'm expecting an RCA Black Plate 6L6GC anyday to replace the preamp's stock Svetlana - hoping for still further improvement.
I'd love to hear my "tweaked' Ref 2 Mk II next to a Ref 3, but that's unlikely any time soon.