"A trivial example would be the thermal heating of a power amp (output transistors, emitter resistors, various portions of the PS) with a sustained LF signal such as an organ note, and then a cymbal crash right afterward compared to just a naked cymbal crash without the prior sustained LF signal. The amp will react differently, and the distortion will be different."

Finally something we can agree on. Although the FTC measurement method requires a preconditioning of operating the amplifier with all channels driven to 1/3 rated power for twenty minutes to heat them up, the changes by sustained high power demands can alter the performance of amplifiers. For one thing, heating is a very real problem with vacuum tubes and bipolar transistors because their characteristic curves change. This shows the enormous advantage properly stablized amplifiers using negative feedback have over amplifiers with no negative feedback since the gain is far less dependent on variables such as power supply voltage and temperature. Non negative feedback amplifiers performance drift all over the place. They may never reach a stable operating condition. It also shows why emitter resistors to prevent thermal runaway in bipolar transistors are so important. It demonstrates that in today's technology, the field effect transistor which is inherently thermally stabalized is the device of choice for audio amplifiers. It also shows the effect of poor power supplies whose bias voltage can be pulled down significantly by sustained high power demands and which may not recover without oscillation or other transient instability when overloaded. The effects of all of these aspects of amplifier performance howerver can be quantitatively meausured using standard methods for IM and Harmonic distortion. What is really required is a change in the test procedure to demonstrate the differences between amplifiers rather than the similarities as we have today. They really have to be pushed to their limit and beyond. No standard test that I am familiar with even remotely simulates the real life operational conditions of driving a loudspeaker and some loudspeaker systems with their high back emf and highly reactive low impedence loads present amplifiers with terrible challenges they are not designed to meet. The caution not to use the current crop of low end A/V receivers with speakers of less than 8 ohms is only the most grudging concession to this limitation of their real life performance. Not that they won't merely perform adequately, but that they are prone to failure under such conditions.

"I really need to do a new paper, and present these to the engineering community as well, before nature or my health put a premature end to my time on this planet. :-( "

I cannot believe there will ever come a time when this board and Cable Asylum will not be graced with your "unique" observations and opinions. After all, only the good die young. Just watch out for a little girl with a dog, three weird friends, and a bucket of water.