After having owned the KGSSHV Carbon for a couple months, I would like to chime in my opinions. First and foremost, an obligatory photo is in order.
Simply put, the Carbon rekindled my long-lost love for electrostats. This is without a doubt the best electrostatic amp/headphone combo I've owned, and arguably the best headphone system I've heard to date.
Now, for some context...
My first electrostatic experience was nearly 10 years ago, at an audio show where I stood in line to listen to the venerated Sennheiser Orpheus. This was out of whim and curiostiy; how would the world's most expensive headphone sound like? I had initially attended the exhibition to listen to stereo loudspeakers, and had virtually zero experience with head-fi. Yet, it was this revelatory 10-minute session that decisively converted me to a headphile. My profile avatar says it all.
However, as I listened to more and more headphones, I found myself becoming detached to electrostats. Not because they were expensive, but they just didn't have the bass impact, oomph, viscerality, PRaT--curse myself for using this term--and toe-tapping factor of a well-implemented dynamic system. They were too polite and ethereal sounding in general for my tastes. I got to listen to the Orpheus again at an audio shop later, but the experience was far more underwhelming than what I had originally remembered. I was excited when the SR-009 (a.k.a. Omega 3, or fish oil) was released, but that excitement soon turned into a major disappointment when I realized it was a unnaturally brighter and more expensive version of the SR-007 (a.k.a. Omega 2) being advertised as more high-end.
After making one of the worst mistakes in my hobby, i.e. buying the Woo Audio WES, I eventually settled for HeadAmp BHSE. It was, at the time, the best electrostatic amp available in the market that money could buy, without going into DIY territory. And I did really enjoy it, especially with the SR-007 MK1, as it was the best electrostatic setup I had heard in terms of technicalities while sounding acceptable tonality-wise. Neither too bright nor dark, just right with a hint of organic warmth.
However, my love didn't last forever, because even the BHSE/SR-007 MK1 left a lot to be desired in the bass and tactility departments. I eventually ended up selling the whole system and started building a dedicated dynamic setup, making my way up to the Eddie Current Studio/HD650 (modded) and Zana Deux Super/Utopia as the best sounding headphone systems I've owned.
And a couple months ago, again on a whim, I sold everything and contacted Birgir (a.k.a. Spritzer) of Mjolnir Audio for his best electrostatic amp. I ended up with the regular, not CC (Certified Crazy) version of KGSSHV Carbon, which had not existed when I had given up my love for stats years ago. He also told me that while SR-007 MK1 was superior sounding th SR-007 MK2 many years ago, the latest MK2 underwent changes and improvements that made it much better sounding, especially with his Blu Tack port mod in place. So I also jumped at a SR-007A, carefully performed the mod per his instructions, and gave them a listen. And boy was I relieved that I made the right choice.
The Carbon/007A (port modded) addressed every issue I had in regard to bass with stats in general. As Birgir assured me with confidence, the Carbon delivered the best bass out of any electrostatic amp I've experienced. Had it been a blind test, I wouldn't have guessed that this was bass coming out a thin electrostatic membrane. Another aspect that impressed me, as many have already pointed out, was how expansive the soundstage was. Although I didn't have the BHSE around for a side-by-side comparison, I don't remember the BHSE throwing such a holographic soundstage, if anything it had a more intimate sonic presentation. This was somewhat counterintuitive because reflecting on my past experience with dynamic systems, amps with tubes in them (be it OPT, OTL or even tube-SS hybrid) tend to have a deeper/wider soundstage than their pure SS counterparts in the similar price league. This is why I tended to prefer tube amps in general, but this was clearly not the case here, and more surprising given the fact that the BHSE is $1-2K more expensive (depending on the pot).
I'm not saying the BHSE is all-around inferior to Carbon. While I found the BHSE somewhat too polite for my tastes, it had a more natural and organic tone that is less fatiguing and pleasurable to the ear in the long run. The Carbon, on the other hand, sounds quite dynamic but does sound a tad bright overall even when paired with SR-007, and being exposed to its relatively aggressive sound for hours does make listening fatigue kick in. If only the BHSE had Carbon's bass, or the Carbon had BHSE's warmer tonality... but I guess we can't always get what we want.
Still, taking everything into consideration, I find the Carbon to be a superior amp overall for my preferences. The BHSE made me miss dynamic headphones, but the Carbon won't. Right now I'm driving the Carbon with Yggdrasil A2, but perhaps a more forgiving source may mitigate some of that ever-so-slight harshess in the upper registers and extend my fatigue-free listening period.
I cannot comment on the T2 because I haven't heard it, but I would definitely love to someday.