Is there actually a difference?

vtvmtodvm:  In other words, perhaps, all amps that have the same characteristics and work within a prescribed set of specifications sound the same.

However, different amps with different characteristics and different specifications will sound different.  For example, my Dynaco Stereo 70 sounds remarkably different than my Cambridge Audio 640 (testing the ST70 with the pre-out from the 640).  My Odyssey Khartago sounds quite different from the 640 driving Harbeths, but they sound about the same driving my Altec Lansing horns.  My HK AV receiver sounds the same as the 640 and the Khartego driving PSB Alphas, but the Harbeths lose dynamics when driven by the HK, and need the extra power from the Khartego (haven't tested the HK with the horns, but I suspect they will sound the same driven by any of my SS amps).  The horns, which I find a bit shrill when driven with SS amps, sound wonderful when driven by tube amps.

Listening is the best way to determine whether you like a particular system.  There is a learning curve, and different systems sound different with different program material.  What you may like (or think you like) is also very subjective.  You are allowed to change your mind.

What a dope Aczel is. Dummer are the people who hired him. How you can have that opinion and be an Audio reviewer  is beyond me. 

If he got better hearing aids he'd be able to hear the difference between amps.

I think the easiest way to hear the differences is by comparing an inexpensive SS amp with an inexpensive 300B amp. I  am hard of hearing in one ear and the other ear is no better yet I can hear the differences. 

@geoffkait —Well, I don't know the answer to your question, but, as (apocryphally) credited to Mark Twain…

“It’s easier to fool people than to convince them that they have been fooled.”

So I guess some people always need more proof.