ok
so to conclude i'd say its like a plane mirror
although it only reflects a selected portion of the reality, one doesnt assume the reality is only the selected portion and may even think theres a conjugative world behind
besides, its only the final waves which directly hit our eardrums that matter, no matter how these waves are generated, by iem? headphones? speakers? they are all assumed the same by the brain if its well simulated
maybe more like the challenge of making a virtual room built by monitors to recreate a real room aiming at fooling our eyes and brains
but ofc i understand same as vr, sound perception is also hard to be simulated especially when the scale is as small as a tiny iem