How can a 40 watt amp outshine a 140 watt amp

I believe in an additional objection to the Richard Clark test method.

The Speaker.

All speakers certainly do not react the same to all loads. I'm not even talking the difference between speakers which have a preference to current or voltage source amps.
Many speakers have wacky characteristics and huge phase swings, even if impedance would appear to be within reason. Worst case? Combine a phase shift of 50 or 60 degrees with an impedance dip to say.....3 ohms. Low power amps or amps which don't like this kind of behavior need not apply. Even if a tube amp would meet Clark's criteria, I'm sure if you compared a heavily capacitive speaker, you'd notice a difference.

Perhaps, when running within limits amps do sound alike, but for some amps and speaker combinations, those limits are either at low levels or maybe even frequency limited. I'd love to hear my panels with 6 or 8 SET watts.

And finally, while I hate to drag Bob Carver into this, I think he demonstrated differences between amps based on Transfer Function. He would somehow connect 2 amps to the same speaker. Any sound the speaker made was the DIFFERENCE between the amplifiers transfer function. After adjustment, the speaker would 'null' and at least for THAT speaker, the amps could be considered identical.

And Xti, the difference between 5k and 7k is negligible. Any manufacturer should be pretty much able to do their best work for that kind of money. Toss something like 700$s worth of Onkyo A-9555 into the mix and see what'cha get. You can probably get the Onkyo for what would amount to a TRUE nutty hi-end guy's pocket change.

Don't forget, Gs5556 (catchy name, BTW!) that the amps under test are NOT run to clipping and are carefully level matched. In real world use, your objection is doubtless correct, but for purposes of this test? I'm less clear.

I think all the evidence needed is in front of us.

First, Carver pretty much proved amps sound different. He had to null his amp to the reference amp to make them indistinguishable. As far as I'm concerned that is 'game set and match' for the 'all amps sound alike' school.

Second, That null was valid ONLY for a particular speaker, though probably close on quite a few others.
The reason? Not only impedance but phase.
Try the same pair of 'nulled' amps on 3 speakers.... 1. A full range, single driver 2. Some Maggies 3. Some B&W from the '8' series.
I'll bet the null doesn't survive all speakers.

Now, keep in mind that the Clark test under discussion specifies NOT clipping the amp(s) under test. A 40 watt amp driving 83 db speakers with an impedance dip to 3 ohms at some wacky phase angle will almost surely clip. I'd be surprised if it didn't, if the level were above 'low'.

I would conclude that using a benign speaker load that it may very well BE impossible to distinguish 2 amps. Stereophile thought they could make such distinctions when challenging Carver. I'd be curious to know if Carver ALSO knew the speaker or had one of the test speakers with which to do his adjustments?

There are many subtle cues to telling gear under A/B tests apart. Even the best poker player can have a 'tell'. I'd suggest that the full test rules have a clue. Perhaps the exact level matching?