I am late to this post, but I have had Don's preamp from the beginning, getting the third one he made, after he upgraded my HK C-I, CII, and C-V's. I have had two upgrades it over the past 4 years and it is back for the latest upgrades at the moment. It is simply the most revealing preamp I have owned in 45 years of having good to great gear.
I also have a McCormack DNA .05 amp, upgraded in 2015 to the Platinum version and it is exemplary. It will be the last SS amp I will acquire. Don has been adamant that his tube amp would be much better than the upgraded McCormack amp I have. I always doubted that assertion as I prefer a tube preamp and a potent SS amp for LF extension.
Well, I got a chance to audition Don's tube amp in my system recently and it took less than 30 seconds to reveal to my ears that Don's amp is even better that the McCormack. Don's amp has all the balls in the LF as well as the high frequency extension, but the soundstage with Don's amp rendered a 3-sound stage, pretty much holographic, compared to the decidedly 2-dimensional sound stage with my McCormack amp. Tonally, they were a push, but the air around the individual players was just palpable with Don's amp, recreating a music experience that was mesmerizing. I have 12-ohm Spatial Audio M4 Triode Master speakers and I can tell you that these speaker love Don's tube amp. It is alway about component matching, of course. After hearing Don's amp in my system, I swiftly ordered one which I expect will arrive within a month.
Those of you that have 6SN7-based tube preamp might well experience a great degree of improvement in sound upgrading to the Shuguang Black Treasure tubes. They are a dramatic improvement over the very good NOS Sylvania, GE's, etc, but of course, much pricier.