And the biggest influence on sound quality is...

One question is, "What, overall, determines sound quality?". A different, but closely related question is, "What, under my control, determines sound quality?". OP tomcarr suggests the importance of the room.

Interestingly, the room is controllable by us in varying degrees. Some listeners may move the system from floor to floor, room to room, some are constrained to one room (but may adjust room treatments), others are confined to one room they can't do much about, and still others have one room and are told exactly where and only where the speakers may be placed.

So yeah. Two different questions, and "room control" floats between the two.

Enjoy.

I liked what Eurorack said about the room.

if I have the perfect room and my source cannot extract all the information from the perfect recording, does the room matter?  I put my money into the best source component I can afford.  
It all boils down to $ and compromise.

Thats my opinion, but that’s usually meaningless 

I think it’s 75% speakers & how they interact w/ the room. 
 

You can have a really good listening room, top quality front end ( analog or digital), amps/ preamps, cables etc but if your speakers aren’t good or at least really to your liking, you won’t be happy w/ the sound.

Conversely, if you have really good speakers that you enjoy, then even w/ a decent room & mid tier all else, the sound will be good & very listenable. Could it be better? Sure but at least you’ve got a system that pleases you. This is not so in the first scenario.

Would echo bigwave1 on Charter Oak PEQ-1. Couldn’t have said it better myself, Dave!

Your system, the whole thing, including the space you're in, is essentially a transcription device.  The synergy there, e.g. the speakers to the space, is something you can optimize.  There is basically nothing you can do about the stuff you are transcribing, maybe outside of cleaning a record.  There are bad recordings of historical importance that can still be enjoyed and listened to, if you're into that, but otherwise you can go more for audiophile quality stuff. I can go either way, but as time passes I find myself more irritated by the simple placement of instruments and the failure of the recording engineer.  As for yourself, the synergy of your equipment is more essential than any individual item, and you're likely not going to get there anywhere near overnight (although it's fun to talk about).