There is something to be said of Nelson Pass as a person. He reminds me of the Grateful Dead, who allowed themselves to be recorded by anyone during their concerts. That is remarkable by any standard. In the same way, he shares his knowledge of audio design and actually encourages it at Amp Camp and such.
When building his B1K preamp, which uses a DHT (SP1), you just can't ignore the great sound in spite of the fact that the SP1 tube is by no means the last statement in tubes. I have actually built other one designers' concept of this tube for a preamp, and guess what? Doesn't sound as good, period. I believe it is because Nelson uses matched transistors instead of an integrated circuit. Anyway, the beauty of kits is that you have more control over what you prefer.
Maybe this thinking translates to consumer products as well?
Don't mean to derail the thread here, as I am interested in other peoples' experience with the big NP amps.