The soundfield, when timbre experience and low distortion are achieved , the soundfield of headphone or speakers had three components NOT ONLY TWO:
---Imaging differentiation of the sound sources one relative to the other...
--- soundstaging dimensions of all sound sources put together... the sound stage must be variable accordingly to each recording... A fixed soundstage is not a good thing in a room or in headphone...A fixed soundstage reflect some lack in acoustic control...Because dimensions of the soundstage must be fixed by each album recording trade-off and location...Not by the headphone drivers or speakers...The shell/cup chamber of an headphone is for his driver in the same relation than the room for the speakers... But because there is NO crosstalk in headphone achieving speaker life soundfield with headphone is VERY difficult... I disliked most headphones because of that... But some headphone are acoustically better than most... There is more than just a driver qualityfor the headphone S.Q. ...
--- Holographical 3-D dynamical perceived VOLUME of each sound sources or of each playing chords...
Immersiveness is the sums of these three factors of the soundfield...
I spoke after my experience and listening optimizing experiments with a dedicated acoustic room and after headphone optimization...I dont speak about a brand name price tag here... But about basic knowledge used in concrete electrical, mechanical and acoustical simple experiments ...Saying that few bucks speakers will be inferior to top costly speakers is only a common place fact without need to be said... Acoustic knowledge is more important than price tag...
I will define acoustically "immersiveness" as a rightful balanced ratio between the "sound source" perceived factor (ASW) in differentiation, dimension and holography and the "listener envelopment" felt factor (LV) , this ratio( ASW/LV ) implicate also that the timbre experience is right to begin with , that the distortion rate is low already and that these two factors are already settled, then if imaging is optimally differentiated and the soundstage dimensions may VARY according to each album recording situation and is not fixed once for all ... If each sound sources own his own volume in space and is not reduced to be a small surface,which i called the holographical factor then Immersiveness conditions are there...
When a system is set acoustically right people forget sound as a negative limitation and are immersed in pure perceived sensible meaning which we call music... Upgrading is meaningless or not attractive anymore...
Then thinking about audiophile sound, dont think first about money, think about basic knowledge and listening experiments... If you want to put no EFFORT and no learning work at all, buy a 50,000 bucks system and call it the best in the world... Perhaps it will be, but perhaps not... Me i will be happy with my low cost mine...