Liquid Amps

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

atmashere, the SIT amps you mentioned earlier appear to be (still) currently available according to the FIRST WATT site. Not sure where to buy and how much.

Atmasphere's suggestion for weighting the type of distortion is excellent.  What's even more important than the type of distortion is where is the distortion located.  Our ears hardly care or notice distortion in the bass regions relative to others.  Most subs have horrendous distortion and are driven by cheap digital amps.  Thus, it's not only the type of distortion that matters, but where the distortion is present too.   

That's why I stand by my original comment.  The speaker and amp purchase cannot be done in a vacuum.  The speaker and it's crossover will play a large role in how the amp behaves and what sound results.  Without factoring in this connection, any universal suggestions are primitive.

As I mentioned, I own lots of stock amps and they can perform well with the right speaker.  However, one can't say arbitrarily that a small amp (like a 10 watt single ended amp from First Watt) that sounds liquid on certain speakers, small rooms, types of music, and/or volume levels will "smoke" a balanced 150 watt amp customize modded for your particular speakers and using the latest and greatest parts and technology (like a modified McCormack circa 2018).

It's really not even debatable and evidences a bigger problem within the hobby than distortion measurements.  Most people buy equipment (and ask/comment online) in a vacuum.  They totally forget about synergy and that's one reason why you consistently hear crap from so many systems with "high pedigree" gear.  It's also why you see such a cottage industry for things such as Autoformers that legitimately can help in some situations because certain speakers and amps are so poorly matched on their own.

Also, the other reason (which I mentioned previously) is that most people skimp on their source which thus creates garbage that no amp or speaker can fix. 

Plus, very few people own a truly full range high end speaker and listen in a room that optimally reproduces music. 

All these other things I've mentioned will impact a "liquid" sound far more than an arbitrary amp recommendation and is probably the REAL CAUSE for the original poster's requested suggestions in the first place.

What's even more important than the type of distortion is where is the distortion located. Our ears hardly care or notice distortion in the bass regions relative to others. Most subs have horrendous distortion and are driven by cheap digital amps. Thus, it's not only the type of distortion that matters, but where the distortion is present too.  

+1 the problem area is seen in the Fletcher Muson curves; our hearing is tuned to be most sensitive at birdsong frequencies, 3-7KHz, where a lot of harmonics of instruments show up, and thus also harmonics generated by the audio chain.

Essentially, this is why tubes are still around- tube amps generally speaking tend to make less distortion that falls into this region.

My subs are older class A/B RELs, and they don't seem to distort in any way I notice, even though they're driven by a 12WPC single ended tube amp signal...efficient main speakers help as nothing has to work too hard, and everything is clear as a bell and more resolving and seemingly accurate than any SS rig I've owned, and I've owned many...atmasphere "guilted" me in to a tube preamp (Schiit Freya) and although I rarely succumb to such heavy handed pressure from his over the top statement which I think was, "tube preamps pick up more detail" or something..."I like it. It's good" (Robbie Robertson line).