Just got my MK3. The volume and bass knobs aren't quite as large and obtrusive as they look in pics. Build quality seems very solid, and I like that the light indicates low battery (unlike the SR71b).
I plugged in my Edition 8s, wired with a TWag v.2 balanced cable. There is a light pop when turning the amp on, but it's much less powerful or bothersome than either the SR71B or Pico Slim's power-on pops.
There is definitely channel imbalance at low volumes, and the sound kind of warbles in and out with some soft static when turning the volume knob slowly between the lowest volume and a normal listening level. The amp is too loud at the lowest, channel-balanced level for my Edition 8s in balanced and low gain (with the CLAS as my source), but I had the same problem with the SR71B. I haven't tested my UERMs yet, but I have a feeling they'll also be tough to find a comfortable listening volume for. There's also a noticeable layer of hiss with no music playing, but it's not too loud.
Using the CLAS as a source, I'm definitely impressed with the sense of resolution, clarity, and realism that I'm getting. Overall, it seems more refined and less veiled than my SR71B was. The MK3's bass seems a bit better defined, and its imaging is less stretched to the extreme right and left, resulting in what I feel is a more cohesive and natural presentation.
As others have reported, the bass adjust knob is very subtle, to the point where I can only notice its effect on certain songs with a constant, thick bass presence. It seems to add a little thicker "shroud" of bass, as opposed to increasing impact. It seems very tastefully done, although I'm sure some people would like it to be more dramatic at its highest levels.
I'm really happy with the MK3 so far, although I would like a wider range of channel-balanced, comfortable listening volumes on the knob. This is mainly an issue with my modern rock/pop recordings, which seem to have a higher baseline volume than my older jazz and classical stuff.
I had to send off my LCD-3s for repair, so I can't test them yet but I imagine they would have a little more usable range on the knob. Also looking forward to seeing whether the bass knob can add a little more weight and warmth to my UERMs and DT1350s...