Are future improvements in Amp/PreAmps slowing to a crawl?

Quite right, Randy. Roger there is basically reengineering the statement that an amp should behave like a straight wire with gain and there's no shortage of failings in that belief, chief among them being that few if any speakers present a purely benign resistive load. The problem with his interpretation of what a volume knob should do is found in the obvious fact that a flute played softly doesn't sound as if it's further away. It sounds like where it's at regardless of how loud or quietly it's played. It's ideas and talk like that which make me implacably skeptical of his claims of perfection. 

kosst_amojan
If you read me post again - word for word you will notice that I don't use the term "should" anywhere in the post.

...that an amp should behave like a straight wire with gain...

or

The problem with his interpretation of what a volume knob should do...   

These statements imply that I am theorizing or expressing an opinion of what "should" happen. That is not the case. In order for me to relate an observation however implies that such a system has to exist. That is the case.

...a flute played softly doesn't sound as if it's further away. It sounds like where it's at regardless of how loud or quietly it's played.

 
This is true but if you are sitting in the 10th row instead of the first row - it does sound further away. Also in the mix is the distance from the flute to the microphone. That is the difference between moving yourself physically at the venue and adjusting the volume in your listening room. Ideally you want the playback volume to match the acoustic volume expressed by the actual instrument(s). Even with no distortion - higher or lower than "normal" volumes will signal the brain that it is listening to a reproduction. If the volume is correct - the brain can accept that it is live

I did a comparison between the Audio Research DS450 and the GS150 at a local shop recently.  GS Pre frontend and VPI turntable via Vandersteen speakers.  Nice setup.  The sound thru the DS450 ($9k), a switching amp wasn't too bad, but, wasn't what I'd call wonderful.  Then the dealer switched over to the GS150 ($20k), yeah, MUCH better.  In fact I brought my daughter along with me and she told the salesman flat out "the 1st amp was Broken..."
Now, one would expect a $20k amp to sound better than a $9k amp.  And, tubes do sound different than SS.  But, at $9k the switcher produced "sound" no magic, no music really.  So, yeah switching amps have a long, long way to go.  The GS150 tube amp, not really sure it could get much better, nor do I feel it would Need to.  Hey, maybe in 50 years switching amps will be as good as modern tube amps are today :) 

Was the ouput level matched to within 0.2 dB?

I can hear a tube from way down the hall. So can the guy under the bridge. No mystery there. 🕵🏻