In my experience everything, every added materials make a difference...
Sometimes positive sometimes not... Sometimes the positive difference was an illusion for sure...
But the only way in audio is embeddings mechanical, electrical and acoustical controls...
Upgrade by gear or tweaks or blind tests are for ignorant or very rich people with money speaking...
I dont need money, my brain is enough to read acoustic articles...
You dont tune a room with Tweaks or blind tests....