Thanks very much for this well written post very well describing what i alluded to in more abstract and less convincing way about immersiveness... English is not my first language...
And yes immersiveness is not only a felt subjective impression but also an objective concept in acoustic and we even had some parameters and science articles teaching us how to reach it in a small room at the times of my listening acoustic room experiments ..
But as i said i lost my dedicated acoustic room...One year ago...
I happily succeeded to recreate immersiveness with headphone which is way more difficult than with speakers in a dedicated room... But i was lucky with the right headphone and the right but long 6 months optimization process necessary for it...
Sound being immersive is an important, even vital trait - depending I guess on the aspect of it one may prioritize or define it as being. Indeed, immersive can be many things, like spanning a contrast range as that which envelopes the listener in a "wash" of sound that takes hold of the experience in its sheer fullness and uninhibited presence, while incorporating moments of intricacies that are more quiet and intimate in nature. Moving closer to a live symphony orchestra can aid an immersive feel, though not at the cost of the whole of the experience (i.e.: sitting too close) - the holistic aspect. It’s a balance, and one I try to live by and apply via my home stereo sitting just on the edge of the radiation bubble. Immersive is about a wide frequency span and being able to use most of the audible spectrum here low and high with full dynamic envelope. It’s as well and not least about size of the sonic presentation, not meant as a "fluffy" spatial image produced by a smaller speaker or one potentially without substance from a panel ditto, but rather one in actual correspondence with the size of the radiation area and overall height of a pair of large, preferably horn-loaded speakers. It’s about bass that can fill the entire listening space effortlessly like a floating, almost liquid presence that just exists/happens - at any desired SPL. It’s about having a coherent sphere of sound that makes the elements of all this come together. As such I find immersive to be a core trait in audio reproduction, and one that’s wholly essential for sound to appear less of a facsimile.