Liquid Amps

The new 25WPC Pass amp does interest my otherwise tube-centric self, but not enough to replace my amazing (to me anyway) Dennis Had single ended tube amp. I still find it interesting that many great SS amps claim a "tube like" sound, which simply supports my tube appreciation. Besides, it's a fact that tubes are more fun (a fact I made up, but hey...it at least "seems" factish).

It's all good "Wolf".  Our Post-Modern world embraces the fluidity of facts.  Yippee!🧐

This is definitely the most liquid looking amp. It is the Von Gaylord Uni. 
http://www.bigpicturebigsound.com/high-end-audio-ipod-he-2006.shtml

Try a hybrid amp. Tube front end makes a difference.  

@atmasphere explains well why it's a little tough to find "liquid" SS amps.

However, there are many issues with tubes too.  I have both SS (McCormack, McIntosh, digital amps, and others) and tubes (ARC Reference), so it's not like I'm prejudiced toward one or the other.

While people are offering nice suggestions and commentary, they are jumping the gun.  We must first know what speakers you are using.

Many speakers have a definitive preference toward tubes or SS.  Thus, any recommendation is primitive without knowing what speakers you are using with this amp.  20 SS watts won't cut it on certain speakers...conversely, certain high power or high gain SS or digital amps will have problems sounding "liquid" with certain speakers (i.e. horns). 

It's actually something that can often be measured.  For example, the output impedance of a certain tube amplifier can pull down levels in higher octaves on certain speakers while boosting the lower octaves.  This could be a good thing and certainly make the sound seem more "liquid".

In short, you really have to let us know what speakers you are talking about.  In my systems, modified McCormack amp are the most "liquid" sounding with my particular speakers...even moreso than my ARC reference amps.  However, I wouldn't guarantee it would do the same for every set of speakers.  Some may like the strengths/weaknesses of tubes more than the strengths/weaknesses of SS.  (I've had Spendor speaker in the past that loved tubes far more than SS.)

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.

It's really amazing what can be accomplished when you get the right pair of speakers and feed it an impeccable source.  An amps strengths/weaknesses can still be apparent, but it become obvious that it's not the driving force behind problems unless you have a really poor amp (or poor combo with a preamp). 

If you're doing digital, the biggest impact on liquid sound is getting rid of jitter.  Focus on the server/renderer even more than the DAC nowadays.  If you're doing vinyl, you probably already know how big an impact the cartridge and phono preamp can make.  Address those things first before thinking a "liquid" SS amp will solve your problem...it can only do so much.