Which component is most responsible?

IMO a general purpose answer to the question is neither useful nor possible. Differences between systems, rooms, recordings, and listeners will inevitably mean that the weakest link has to be identified on a case-by-case basis.

FWIW, though, if the question were re-phrased to be asking what factors generally have the greatest possibility of adversely affecting "separation of voices in a chorus or when listening to multiple background vocals," given that you are using a digital source, IMO the answers would be the recording, the speakers, and speaker/room interactions.

Regards,
-- Al

source

LOL! This thread is beginning to remind me of that old Why the rectum is the most important organ joke. ;)

Jmcgrogan2, haven't heard that one in a very long time, guess it's been around for years.

This thread is reminding me about reading this some time ago,

Put 10 audiophiles in a room to discuss a topic, and they will emerge with at least 11 different theories.

"12-18-13: Quad-man
I would rate in this order: The recording..source..pre-amplifier...amplifier....speakers.

The speakers are often the most innocent...unless they're not!

Another way to look at this: all in all the pre-amp in the most responsible."

Its good to see that so many people are giving preamps the credit they deserve. This wasn't always the case. Preamps are often overlooked when building a system. They're just as important as any other piece.