And the biggest influence on sound quality is...

+1 @knotscott 

I took your question to mean building a system, so I would answer absolutely

the speakers and the speakers........

With the room a close second.

Regards,

barts

Less than stellar recordings you can make better using for example the Charter Oaks PEQ-1. Would not live without it. An amazing piece of gear IMHO. 

I know it's the room but when I told my wife I wanted acoustical panels on the ceiling well then................

@tomcarr you covered most of the ones that really matter a lot. I’d add the proper technical integration of components when dealing with separate as opposed to integrated components like impedance matching and also that amp is a good match to drive speakers to their max. Poor matching and integration of components can leave a lot of performance on the table. This is a very common snafu that many may not pay as much attention to as they should.

Of course in the end it has to sound good to your ears specifically and that can be a very subjective thing to determine.

After that its mostly a tweak here and there perhaps. Modern DSP technology is your friend when it comes to getting that sound just right once you have crossed all the Ts and dotted all the Is in assembling and setting up your gear well. The icing on the cake!

The other things are all significantly big but room acoustics always plays a big role in how things sound (pretty much by definition) and is typically the thing you have the least control over.

Recordings are what they are. You have absolutely no control over that. You can only attempt to experience the works of others as provided as best possible.

Fun fun fun!!!

Quality of recordings are very important.