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You are dead wrong....as usual

And if you want to know the relative merit of the output impedence of an amplifier, look at the damping factor. It is defined as the load impedence divided by the source (output) impedence. It's usually specified at 8 ohms. It tells you everything you need to know about an amplifier's ability to control the motion of a speaker cone. Most solid state amplifiers have far higher damping factors than most tube amplifiers. Right now the current champion is Crown Reference series with a rated damping factor of 20,000 at 8 ohms. Looking back into it, it is effectively a dead short against back emf. BTW, this same principle is critical to damping the motion of rotary motors as well as linear (loudspeaker) motors. In that application it is called "dynamic braking" and is an integral part of many large motor control circuits. As for the impedence through the feedback loop it is many orders of magnitude higher since it is not required to drive any appreciable current through that circuit. In fact, since the amplifier creates voltage gain but the feedback voltage must be comparable to the input voltage or an early stage voltage, the feedback impedence must be even higher than the input impedence which is of the order of many kohms. Stick to chemicals.

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