Yep! Here i am. The bread crumbs in the butter!
Kurt, I have to ask about your experiment to listen to just the surrounds during movie playback. Which movies were they? And more so, I’m sure you know that’s not really a fair test. As the information in the surround channels is discrete it is also supposed to work with the center and mains to form a cohesive sound field. IMO, your test was like checking for stereo imaging with 2.1 with only one speaker.
I don't really remember. I know one of them was an Avengers movie (the one with the flying aircraft carrier).
My test was not to evaluate the sound quality of the surrounds; it was to evaluate the content. At the time, I had Paradigm Signature S-2's as my mains and the Mirage OMD-5's for my surrounds. I was already comfortable with the sound quality of the Mirage speakers. I had happily used them for music (and, later, as surrounds). Certainly, side by side, they sound about as different as they could from the S-2's given their omnidirectional dispersion.
What I primarily remember hearing while listening to the surrounds alone was very muffled speech (ambiance from the dialog), indistinct crowd/traffic noise, falling debris, ricochets, rain, etc. There was nothing that would be distinctly definable by me as inappropriate if some nuance of the sound wasn't quite right. IOW, it may be the case that the sound of a ricochet is not exactly what it should be for the specific caliber of bullet glancing off of a specific material, but those are not sounds I know well enough that I would ever hear anything wrong.
If there was a scene where the point of view was from someone in a straight trench looking at the enemy (perpendicular to the line of the trench) and the person directly to either side spoke to me,
then I would get much more interested in making sure the surrounds were a very close match to the mains. Human speech is a sound that we assign audible characteristics to critically. However, I have never seen a movie do this. The camera always pans to the person who speaks even if the reality is you would not look at them because you are sighting down your rifle waiting for the enemy to expose himself!
If you know of a movie that is particularly demanding of the surrounds, I would like to check it out. However, IME, I have yet to watch one where the surrounds have critical content. Although I suspect there is at least an experimental one or two out there.