Liquid Amps

@hifiman5 
Slightly off-topic but wanted to chime in on your observations on the Sutherland KC Vibe. Being such a new product there were precious few reviews, but I too bought a unit based on Ron’s pedigree. 

In my my somewhat modest system, I started off enjoying the sound — beautiful, forgiving and slightly polite. It was only in comparison with other (more expensive) units that the Vibe was revealed to be somewhat closed-in and rounded off, leading to the initial perception of “warmth” and lack of nuance/detail. 

I put this down to synergy and went with another option instead, but am glad to read corroboration of my experience....perhaps it is the nature of the Vibe after all. Guessing it is a conscious choice of the designer to hide flaws of more modest systems, which speaks to your point of system matching. 

All this being said...I don’t think the BIGGEST problem with systems not sounding "liquid" is the fault of higher order distortion in SS amps. I don’t think Atmasphere made the claim that it’s the "biggest" problem either, so we may not even disagree per se. I just want to point out that IME the biggest problem with systems not sounding "liquid" rests with the speakers and source first...not the amp.

If the speaker is more revealing, it will totally play the distortion that makes many solid state amps sound bright and harsh.
This distortion is not a lot as far as test instruments are concerned, but to our ears it is, which is why its so easily heard (and why tubes and tube amps are still around decades on after being declared ’obsolete’; if they were really obsolete they would have ceased production long ago).

The real problem we are dealing with is that the audio industry (like many other industries) does not like to deal with inconvenient truths. In this case it is the fact that our ears, while seemingly inaccurate and insensitive to so may aspects of audio, are more sensitive than the best test equipment when it comes to detecting higher ordered harmonics.
BTW this is extremely easy to prove with very simple test equipment!
Anyway, IMO the industry should put a ’weighting’ (like we do on noise) on harmonic distortion. Less weighting on lower orders, higher weighting on higher orders (particularly the 7th) so when you look at a spec sheet, you can finally tell what the amp will sound like! Right now, the spec sheet has marginal usefulness (unless you keep a bird or hamster) since it really doesn’t tell you how the amp sounds. And ’liquidness’ is all about how the amp sounds.
Some solid state designers get this- notably John Curl and Nelson Pass. Both will freely acknowledge that tubes still rule the roost as far as liquid or smooth sound is concerned. I think Nelson has done more work in this area, and the amp I mentioned is easily the smoothest solid state amp made.
BTW I think the McCormick is a very good amp too, but the little VFET amp Nelson came up with totally smokes it in the smoothness/liquid category, without sacrificing detail in any way. Of course, tubes do that too :)

Lets not forget Vandersteen's liquid cooled amps

@stringreen , 
let me add something even more bizarre : we have Von Gaylord's World First Liquid Cooled Triode Amp , how is that for a change!! 

Throughout their history, Von Gaylord (formerly Legend) tube amplifiers have produced some of the best sound I’ve encountered. One could certainly use the word liquid in describing them. Beyond that, I normally dislike the sound of 6550 amplifiers. These amps obviously know how to wring especially good sound out of that tube