Just about everything has some kind of influence on the sound.
I noticed differences with room treatment.
Sourced from GIK in the form of 4 tri corner traps, and two full bass traps and ASC and DIY on walls.
Next and of the same importance was anything I did to improve the power to my system.
This includes dedicated lines, power cords, power cord receptacles, wall plugs,fuses and wire.
Then a really good equipment rack for your gear.
It was only when I went this three-way route,that I started to really hear my system.
If more people tuned into this, I think there would be less instances of comments like" I never heard a difference".
I believe it's hard to tell one upgrade from the last if the system is restricted in any of the three areas mentioned above.
Unfortunately, new amps or speakers are always first on everyone's fix it list.