Ultimately, recording quality and room will define the limits, but I am talking about top level equipment. In your average $50k system I am not sure which component contributes most. But I belong more to source first school, so, I guess, it's either the recording or "transport", be it turntable itself, cd transport or tape deck transport. Poor recording will sound like junk anywhere but with average recording the better your set up is the better it will sound. It's a continuum from very poor to great recordings, and I think the answer to the question is more complicated than this or that.
And the biggest influence on sound quality is...
The quality of the recording itself.
Then the room, the setup, the speakers, and lastly the front end.
I've got recordings that make my system sound horrible, and I've got recordings that make my system sound absolutely wonderful.
None of the gear changes have had that much impact on sound quality.