Is there actually a difference?

As a former commercial property appraiser, I appraised 17 sound studios in Southern California.  Many of the studios had high end playback gear.  Same with my friend Robert Pincus, record producer, who visited various major label studios.  They did not use junk pro gear equipment in the 80s or 90s.  Two studios used my Legacy Focus for playback. Sony used big B&W800d2 for playback in NY.  I didn't check their cabling which was probably standard issue balanced and heavy duty A/C.  Most of the studios had superior power conditioning.  I remember one had 22 isolation transformers of 2KV each (former use was for tube computer equipment for BofA accounting).  

Interesting read on this topic here:

https://www.dagogo.com/audio-by-van-alstine-abx-comparator-review-part-3-new-twists-conclusion/

The reviewer can pick out cable differences much more easily than amp differences.  In fact, as long as the amps are level matched, he couldn't distinguish a tube amp from a solid state amp.  

Alan Shaw of Harbeth makes a similar point, although he is often misquoted as saying "all amps sound alike."  He actually claims that level-matched comparisons between properly functioning amps within their normal operating capacity will sound indistinguishable.  If they don't sound the same, then they are not level matched or are producing distortion (pleasing or not).    

No, no, no.  Amps can be level matched and sound totally different.  The amps have to match the requirements of the speaker.  If the amps sound the same (possibly Harbeth), then the speaker is probably an easy load.  My speakers sound vastly different as do many high end speakers based on the amplifier's characteristics.  Difficult load speakers due to impedance, phase angles or sensitivity present all types of challenges for amplifiers.  

@fleschler We're actually saying the same thing.  Shaw's point (as I understand it) is that a speaker needs to be matched with an amp that can drive it without significant alteration in the amp's output. A 20 watt tube amp and a 250 watt solid state amp will sound different on a speaker of moderate sensitivity with a difficult load.  However, that difference is due to the tube amp's interaction with the speaker's impedance curve. If both of the above hypothetical amps were paired with a speaker that is high sensitivity and an easy load, they will both sound remarkably similar in blind, level-matched tests.  

You say "My speakers sound vastly different as do many high end speakers based on the amplifier's characteristics. Difficult load speakers due to impedance, phase angles or sensitivity present all types of challenges for amplifiers."  

Agreed!  But the idea is that an amplifier that can meet that challenge (and why would you want an amp that couldn't?) will sound largely indistinguishable from any other that can drive the same speaker without difficulty.  Blind, level matched testing seems to bear this out to a surprising degree.  

"Alan Shaw of Harbeth makes a similar point, although he is often misquoted as saying "all amps sound alike."  He actually claims that level-matched comparisons between properly functioning amps within their normal operating capacity will sound indistinguishable."

Tell him it is true for speakers, too. Take his blood pressure afterwards.