After a failed experiment moving from tubes to a Devialet-based system, I punted a few months ago, sold the Devialet, and have painstakingly rebuilt my system. I am currently auditioning the 508ia as the final piece of the puzzle. The fit and finish of this amp are astonishing at this price point, and even with less than fifty hours on it, it is clear that this is a special amp.
For those of you who have rolled in NOS tubes--especially the 6SN7 and 6SL7 tubes--what have you tried? As you would expect, the stock tubes--Electro Harmonix and Sovtek--are a little bit on the hard or rough side, although some of that is no doubt due to the low number of hours on it as well. I'm thinking some good old Sylvania Bad Boys or Tung Sol round plate black glass might just do wonders for this amp, but I would love to hear what others are trying and liking.