I appreciate your expressive and varied way to articulate what you hear.
Perhaps you can comment more on the few clips I've excised above.... It can be fun but challenging to read into someone's language to imagine the sound itself. And useful, given that we order without hearing, usually.
I've found that people (sometimes me) can get several concepts mixed together. "Speed" is a word that I usually distrust, because some people mean "bright" or "peaky" or "emphasises transients" (as in transient distortion). Others mean "the other headphones are muddy or inarticulate sounding." "Speed" isn't something one can hear directly (like "treble" or "trumpet" or "body") because it is a characterization of a transducer, not of music. It's an "engineering" term not a musical one. So, there is quite a diversity of what people might mean.
You are describing a different sense of air than I use, but a useful one. (I usually think of the way the triangle hovers over the orchestra and makes you feel you can "hear the air" over the orchestra rather than being black or smeared and indistinct.) I like the idea of space around instruments being reproduced well, something that takes good accuracy or transparency to do, an illusion based on low-level details and thus easily destroyed.
Yet, I've too often found components praised for "detail," to pick a different example, when in fact what is happening is a peakiness that spotlights a band of frequencies that trigger the idea of "detail."
You used the word "etched," which I hear in two ways. The way it can be used that I don't like the sound of is detail emphasis over body and integration into a liquid total soundfield. Treble dominating midrange, sometimes.
But I think you mean a distinction of boundaries around instrumental images.
I was also curious that you mentioned the LCD-2 sounding more "analytical" than the HD800. I find the latter enthralling intellectually, given the soundstage size and better detail than my HD650, but also unmusical due to the treble emphasis band, such that it saps the joy out of listening. So, I'm looking to understand your use of the word "analytical" in this situation.
In any case, you are helping me get a sonic picture of something I am interested in perhaps buying. Tx.