The way we listen to speakers has nothing to do with the way they are designed. They are designed to be transducers; you can use them anyway you wish. The information for the stereo effect is embedded in the recording, and has nothing to do with the speaker.
Let's say you have a stereo amp and two KEF coax speakers. You want to upgrade to 7.2, so you go out and get a 7.2 receiver and 5 more of the exact same speaker. That speaker doesn't know that you just went from 2 channel to 7 channel listening. Because of the electronics, not the speaker, it will work just fine.
Perhaps you want to listen to Ambiophonics. Ambiophonics normally uses, I believe, 12 speakers. Those speakers would not be any different from your KEF speakers that you used for 2 channel listening. Again, that design will work just fine.
In my mind, the speakers that have been mentioned as taking stereo into account in their design, like the Bose and the Polk, were experimental. I've heard them. I was not impressed. They yielded no improvement to the majority of listeners, and the majority of listeners is what provides a company with income. As for speakers with offset tweeters, the vast majority of those were offset to either mitigate diffraction effects or deal with crossover nulls in what the designers may have thought were "normal" residential rooms. Although there were a few (the minority) that were advertised as being offset for the purposes of "balancing" the "stereo effect", that was something that the advertising department used as an advantage. To go back to the analogy of reviewing cars, a car with suicide doors will not drive differently, either on the track or across town, even though the door symmetry is different.
And one last point, if I may. Where has anyone printed anything regarding listening to one speaker and predicting how it will sound for stereo effects set up in a 2 channel listening setup? If I am wrong, please point it out to me, because as I see it, that is a straw man argument. Speakers are tested for function as a transducer. If they have a peak (or shelf) at 5KHz, then listening will reveal that they sound either harsh or bright. If they have a dip between 200 and 500 Hz, that is noted, and listening will reveal a "hollow" sound. No comment is made about how that affects their sound in, specifically, a 2, 4, 5, or 7 channel setup. The brightness or the "hollow" sound will show up in any or all of those setups. The stereo effect (or the sound effects in movies) will still be there, and still be the same, effects-wise, as on a different speaker.
The strengths or weaknesses of a speakers are strengths or weaknesses as a transducer, not as strengths or weaknesses as an instrument of spatial effects. Again; those spatial effects are in the recording.
Jim Taylor