You say that you have no idea what "an acoustically dedicated room is" and i know myself what it is... Then...
Speakers in a living room dont compare to the same speakers in an acoustically designed room... Electrical/mechanical/ and acoustical embeddings dimensions must be under control...When they are, the same speakers work on another level completely...They are unrecognizable even if their basic technological limitations in frequencies dont change for sure...Acoustic is basis of audio experience....
I know that because i did it myself... :)
My point was about comparing RAW unmodified headphones and unmodified speakers generally, and generally speakers in living room,( acoustically dedicated room are not and never mere living room,) dont beat the best headphones on all acoustic factors...
For sure it is relative to specific quality scale : a cheap headphone dont rival a high end speakers...
My point is about very high quality headphone versus speakers in a living room...
If the same speakers is in a dedicated acoustic room designed for it, it will rival or beat most headphone, but it is also related to the specific headphone price sound quality ratio...
My point in this thread is about my OWN experience going from a specific pair of speakers: Mission Cyrus 781 from an ordinary room to an acoustically controlled room... I lived through a complete better performance with this speakers...I was in heaven...
But after loosing my house i was in the obligation to go back to headphone to my displeasure at first...
But i used the AKG K340, i modified them after 6 months of experiments and my surprize was that this headphone beat my speakers now... On all acoustic factors...
Then it take high end speakers ( better than my past Mission) in a dedicated room to beat very high end headphone...My Mission speakers only with bass frequencies never go very low under 50 hertz , my K340 go under 30 hertz... Only that tell a tale... The electro-acoustic cell of my K340 give me better high frequencies too.... And the 3D "out of the head" soundfield of my modified K340 rival my speakers/room...
Then i am no more sad to listen only with the headphone...It will be very costly to replace them...