Supra upper mids/lower treb? Are people always working on that part? Ken Rad black glass 6SN7's? Hmmmm....Has anyone listened to how Kondo deals w/ upper mids/lower treb while still maintaining dynamics?
Not me!!!!
IMO, this is too much to ask solely from the preamp. The Supratek is not a magic tool. It is a very good preamp but needs to be mated, to maintain synergy, with good components too. The preamp is now telling you the truth about the systems shortcomings base on your preference and you have to single it out as the culprit? Not wise IMHO!
For the record, I too was dragged to "tube rolling" here regarding how much improvement you can benefit from it. In fact, I fired some of my recommendations as well while I am at it. But in all honesty, as I mentioned before trying to report about how good the preamp really is without canging anything but just waiting patiently for it to settle, the stock tubes that Mick shipped are the tubes where the preamp is calibrated. Granted that not two people are alike, it might be wise to let the thing run for a while before constantly buying and replacing the tubes to tailor the sound. So far, the only tubes that I replaced that I am succesful are the two 6C4 tubes in my Chenin.
Been there, done that, never again! FWIW, did you guys noticed long time Supratek owners in the last 3 months (myself included)un-loading here at Audiogon NOS tubes they accumulated and found out they do not need? My point is, some of us got so carried away from recommendations of such tubes and when the dust settled found ourselves in full circle journey by accident. That is, putting back all the stock tubes shipped with the unit and was shocked that the preamp sounds better with them than the costly NOS tubes.
Of course, YMMV and I am just reporting my experience.
cheers