Hi, I find the BHKs extremely natural, transparent and very clear sounding. I find it difficult to imagine anyone feeling that they lack clarity in the high end, but perhaps these listeners are looking for a more aggressive and accentuated high end.This might relate to their loudspeakers not being as transparent as the SoundLabs, or perhaps their associated equipment as well as wires. And of course, there is always the differences in personal taste. I am using the top of the line Audioquest speaker wires. I find that my whole system is very revealing of the differences in program material and of course I do not know what these listeners might be listening to in terms of program material as well as sources.I am currently listening almost exclusively to vinyl, however when I listen to digital, it is CDs through an MSB DAC and transport. Although some listeners feel that streaming delivers the same quality as CDs, this is not my experience, even with higher quality streaming. And of course less than the best streaming, which many people listen to, and lower quality DACs, of course, might be an issue with some listeners experiences, and they might be looking for “bright” electronics to juice up the high end. I like it natural and believe me, with my system, there is no problem with high end clarity. In terms of the tube rolling, this of course can make a difference. Honestly, as I had the Bugle Boys around, I switched out the tubes as soon as I got the amps, so really have no experience with the stock tubed. There are some other tubes PS recommends, I believe Tungsram. In terms of why there are so many BHKs on the used market, I don’t follow this so I was not aware and really have no explanation. Perhaps there were a large number sold and so that may relate. I believe that PS has a return policy so that would enable you to try the amps in your system. BTW, I have also used the BHKs with the Triton References that I designed, and they sounded excellent with those as well.