Would you distinguish between the "big panel sound" and something like an ESL-63 that radiates more like a point source? Or do they both have common colorations to you?Having some Harman speakers and ESL's in the same room can be somewhat enlightening. The Harman designs do seem to be more transparent and get out of the way of the music more than the ESL. It primarily comes through as a perceived FR difference. This seems so on things I've recorded and know what the sound was like.
It is worth noting that a speaker meeting the guidelines from Harman avoid any significant resonance. So the boxiness often perceived in box speakers is low in level if not absent.
In a position to switch between them pretty quickly the valued qualities of the ESL don't seem much in evidence though a coloration does.
None of this has been rigorously pursued much less probed with extensive measurements about how the dipolar radiation interacts with everything else.
Yet, put the ESL's in a room, listen to them, and you'll be enjoying them. Of course I also enjoy the Harman box speakers too. Enough that it makes me question if putting up with the care and feeding of big panel ESL's is worth it anymore.
My last ESLs were 1+1s, which were sort of a pseudo-line-source.