Where to upgrade next? Need critiques of my vintage setup.

That's of course assuming you feel that amplifiers are best evaluated via ears. I prefer to make assumptions about necessary frequency response, power output, distortion characteristics, etc, and then measure. A final evaluation must be performed by listening, but during design and construction, it's better to let the math do the talking.

 

I concur. They have to measure right along with being properly engineered. Then one hopes to tune them to sound great. Ear evaluation is a big part of what high end audio is all about. High end audio wouldn't exist if we couldn't here the 'improvements'. We would still be listening to perfect measuring Japanese gear of the 80s.
Great audio design is a balancing act. Sadly, there there are many commercial companies out today there that still haven't attained the goal.

Cheers, sir.