Most people dont realize the degree to which acoustic and psycho-acoustic dictate everything and the manys way which you can use it at will in a room...
It is impossible to understand without playing with active mechanical control and not only passive materials treatment...
For example to reach this " Headphone effect out of my head" i spoke above in my post above , i was using the frontwave law of Has and Helmhotlz resonators and i used an acoustic wood screen (with some absorbing and diffusing parts) in two parts with a variable angle, i placed it between my back and the two oriented speakers which are controlled by the resonators dyssimetrically for each of my ears using in this way Has law of the first wavefront differently for each one of my ears......
Then when i listen it has the intimate effect of headphone but filling my room at the same time like if it was just outside my head...Difficult to describe...In some recording i can hear voices or instruments even behind my back but generally the sound had the depth out of the speakers floating almost all along the width of the room just outside my screen...
i placed forever my 7 pairs of headphone in a drawer...Not one is on par.... 😁😊
I only wrote this to advise people to READ about acoustic...Not about upgrade...