Must speakers have certain volume to sound convincing ?

Stradivarius will sound great in anyone's hands just as great speakers will sound great regardless of what kind of junk they are forced to play by some so-called audiophiles and giftless musicians.
It's quite telling that no-one so far asked me why I think panels don't sound real. In any case, that notion of mine was not the main line.
It also appears at the moment that what I said about proccessing of perceptions may be an incomprehensible remark. No matter, let's continue with usual bullsh-t.

One hears with their brain not their ears. That was my point early on. We are all slaves to our experiences, education and preferences built over our lifetime.
Also it was mentioned "assuming good hearing". I would bet our hearing abilities across the frequency spectrum are all over the place...collectively. "When is the last time YOU had your hearing evaluated?" I agree with asvjerry. Also the set of preferences, qualities or the like ....with what sound should be is also different for everyone. Each of us will place a higher or lower value on such tags as "soundstage, dynamics, bass depth, etc"

Your hearing is only as good as the best HiFi system you ever heard. 

"Stradivarius will sound great in anyone's hands "--this simply is not true.  It takes years to learn to produce a good tone and to play in tune on the violin.  And not everyone who tries achieves that goal even with the years of effort.  So, no, it's just not true.

Right. We live for the chase and thrive on arguments.
Never played Stradivarius but once I did play a very high level custom classical guitar. It sounded spectacular, and my skill as a guitar player is rudimentary. True, violin is a more difficult instrument than guitar or piano, generally speaking, but I am quite certain that this makes no difference. I heard excellent violins played by lousy musicians.