Best 12au7 type I ever found for the minimax pre was a triple mica, 1950s Raytheon blackplate 5814WA, which even bettered the outstanding Amperex 7316 PQ, which is also a fantastic tube.
Wish I were getting one of these new dacs, but can't swing it at the moment. I'm looking forward to what the first round of users have to say about it though. I've owned many EE products and they have always been outstanding, solid products that perform way above their price.
-- Jim