Is there actually a difference?

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).    

@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.