It is an extreme example I used to show how level matching at a spot frequency and capturing a voltage based recording at the speaker terminals is flawed. It doesn't take into account how that speaker will sound when driven by the system as a whole, on musical content, and how two different amplifier configurations that produce the same spot voltage at one arbitary frequency at the speaker terminals, can vary in their overall acoustic response in that same room. A small change in FR could easily activate a room mode and make a large change to the perceived sound. That is a real audible difference.
This discussion is about a BTL amp vs the same amplifier in single ended 2 channel mode and any
audible differences into a single pair of speakers in that room. Electrical measurements are absolutely irrelevant for audibility determination in this situation, except for initial level matching, and that needs to be done with access to the loudspeaker's impedance/reactance curve to pick a worst-case load frequency and match to that. And you know me, I love measurements.
I never closed my mind like so many others to the notion that amplifiers might sound different to one another, and also devised many experiments and configurations over the years to prove to myself that they actually sounded the same. Trouble is, they didn't.
And we have individuals stating amplifiers sound the same* as if it was some accepted science and completely beyond questioning. Where is the research? Seriously. I have books, magazines etc from the 50s onwards until now, across electronics, HiFi, music, you name it- where is the research? And when questioned, the first thing to do is poo-poo the attempt, but offer no reseach/experiments of their own.
The amplifiers are at the end of the chain. Everything else gets it easy. No large currents, high voltages or difficult load angles for the rest of the system. The rubber hits the road when the speaker makes acoustic output. And the amplifier does all the work. That interaction is the most complicated and yet is gets the least attention. Funny that.
* when operated at a similar output approaching, but below the threshold of clipping and without gross flaws in FR or audible levels of THD.