And the biggest influence on sound quality is...

If you're just getting started, the speakers and room are the places to spend your resources, but at some point it all matters.  Once the system reaches a higher level, you need to more careful to match anything new that gets added to the system level or it'll become the weak link....and the weak link is usually matters most.  

1. The room. A modest system in a great room can sound great whereas a great system in a bad room will sound worse - the wider you open the window, the more much flies in, as the saying goes.

2. The system - at the risk of repeating myself across various threads, systems are called systems for reason - it is the quality of the individual components but also how they do or don't work together as a system.

Recordings are what they are. A great system in a great room will make a bad recording listenable. A great recording on that system in that room will sound wonderful.

A great recording on a bad system in a bad room will sound "meh" at best.

...a glass of great wine.

Quality of the recording because it sets the ceiling. You can reach it or you might fall short of it, but you can’t exceed it

1. The room. A modest system in a great room can sound great whereas a great system in a bad room will sound worse - the wider you open the window, the more much flies in, as the saying goes.

2. The system - at the risk of repeating myself across various threads, systems are called systems for reason - it is the quality of the individual components but also how they do or don't work together as a system.

Recordings are what they are. A great system in a great room will make a bad recording listenable. A great recording on that system in that room will sound wonderful.

A great recording on a bad system in a bad room will sound "meh" at best.