I have been listened to the GS-X mk2 for the last week and find myself very impressed. Nearly all my listening is using a Lavry DA-11 DAC and HD800 headphones. I mostly ran fully balanced, but I did do a brief sighted A/B comparison between running the HD800 fully balanced and through a 3 wire 1/4 plug.... honestly, I didn't hear a difference. Source material is mostly loseless 44/16 though I have a few higher resolution tracks. Musical genre has been a wide range: classical, folk, bluegrass, jazz, rock, electronica.
Summary: The GS-X mk2 is the best solid state amplifier I have heard with the HD800 -- this is relying on memory not A/B. I the past I have had a chance to have extended listening to several great amplifiers which have included B22 fully balanced, Dynahi, Bryston BHA-1, and Apex Arete + Volcano. Lifestyle keeps me away from tubes, but I like the GS-X mk2 better than most tube amplifiers, though there was a modded Eddie Current SS7 I listened to which I think would give the GS-X mk2 a good challenge. For people who have heard other Dynalo or Dynni amplifiers, I would say that is the same, just better, in every dimension.
I have spent the most time comparing it to my Headamp GS-1, but I had a one day "Headamp" fest with Gilmore Lite with ELPAC , Pico Power, GS-1, GS-X original, and a GS-X mk2 in the rack. In other people's reviews I read that there was more of a difference between the Gilmore Lite and the GS-1, than being the GS-1 and the GS-X. I found this to be the case with the original GS-X, but I found the difference between the GS-1 and the GS-X mk2 to be as dramatic as between the Gilmore Lite and the GS-1.
At some point I will try to take the time to work through my notes for specific examples, but for general impressions:
Bass: Tight, Controlled, GREAT detail, Good impact. I have heard some people say the HD800 properly amplified has good bass control and tone, but are a bit light in quantity. With the GS-X mk2 there is no issue with quantity.
Mid: Smooth but with great detail. Doesn't have the warming of tubes, but very engaging.
Tremble: Better extension that any other amplifier I have heard. Crisp and crystal clear without being shrill. There are several tracks that seemed a bit to bright when listening to the HD800 with other solid state amplifiers. Somehow these tracks are more listenable for me on the GS-X mk2 even though there isn't a roll-off which is damping things down. Don't understand, but I am enjoying it.
Sound Stage: Amazing!
My "problem" with the GS-X mk2:
Between the time I ordered the GS-X last fall and it arriving I switched from having the HD800 being my end-game to SR-009. The HD800 generally won't be used in my living room, they will do office / "transportable" duty. I was planning on giving the GS-X mk2 a listen, and then sell it, because it would sit idle in my living room. Now that I have spent a week listening to it, I am not sure I am ready to let it go and am tempted to move it to my office, even though it's overkill there since I mostly work with music being more background than foreground. I really like how this amplifier and the the HD800 sound. I am even having second thoughts about the SR-009. I have been using a friend's for the last two months while he has been in Japan. I was going to send him money to buy my own pair just before he returns, but now I am wondering if the GS-X mk2 + HD800 might be my end-game in view of other things I could spend the money on. I still think the SR-009/KGSSHV is a step above the GS-X/HD800, but sometimes money is better spent on things that aren't headphone related.
--Mark