Hi Al (Rodman),
I think that your points are generally well taken, and I realize that they are backed up by a great deal of relevant experience.
The one point I would make in response, though, is along the lines of Kijanki's comment. It is often said that the power supply and the power source are in the signal path, and that is certainly true in a sense. However, as I'm sure you realize but others may not, the effects of power anomalies on what ultimately goes into the speakers (or at least those effects that are explainable based on generally recognized science) will be greatly reduced by filtering and smoothing that is provided in the power supply, by filtering that is (or at least should be) provided at or near all circuit points where the outputs of the power supply are used, by the
power supply rejection ratio of the circuit stages that directly process the signal, and in many components by voltage regulator devices and circuits.
I think that a good indicator of the significance of the distinction between being directly in the signal path, and being indirectly/in a sense/sort of in the signal path, is that if this thread were about fuses that are in speakers, or fuses that are in amplifiers in series with their outputs, I suspect that it would have ended about 300 posts ago, with little or no controversy. I, and I suspect most technically-oriented fuse skeptics, would consider it highly surprising if there were NOT significant sonic differences between fuses in those applications.
Best regards,
-- Al