Ears. None of this really matters without 'em. :)
Second most important is room.
No system will sound good in the wrong room I don't care what components you have.
Third - When it comes to electronics, speakers are the most important. Yes.. yes.. I know.. garbage in, garbage out but if you have a great source and garbage everywhere else, you still get garbage doncha? Speakers establish a dimension of possibility within a system - good speakers with garbage components can still sound nice (with the right cables) but... take a pair of crappy speakers and hook them up to any system you want and it ain't going to sound pretty.
Second most important is room.
No system will sound good in the wrong room I don't care what components you have.
Third - When it comes to electronics, speakers are the most important. Yes.. yes.. I know.. garbage in, garbage out but if you have a great source and garbage everywhere else, you still get garbage doncha? Speakers establish a dimension of possibility within a system - good speakers with garbage components can still sound nice (with the right cables) but... take a pair of crappy speakers and hook them up to any system you want and it ain't going to sound pretty.