Which component is most responsible?

Of course it must be on the recording first, of current recordings the wonderful Swedish choirs on BIS lead the pack IMHO.
After that its the preamp and it not be an expensive one, the Hafler DH-101 was good at it as was Nikko back in the day.

I keep a Bryston BP-6 around for the sole reason it is stellar at this, though my EE Avant trumps it in about every other way. Of course if you use Vinyl the cart must be up to it as wel, I switched to a Nagoka MP-200 from a Grado Silver for that reason.
Any of the usual suspect 300-500S monitors will do what needs to be done.

The best recorded choral CD I've heard is BIS CD-533 "Christmas Music" featuring the a capella male chorus Orphei
Dranger of Upsulla University.
Its not all Christmas music and its not all in Swedish,but is all magnificent. Three male voices alone singing the "Coventry Carol' made my hair stand on end.

Straight up gang, the Swedish Choirs are the worlds best and the BIS label makes the best Recordings extant.

Davide 256, I think we all know that. The 3 voices are 1 track of 16.Carmina Burana is miked for what it is, an exercise in vulgarity.
But then I am at fault for not mentioning that the Choir of a major European University, with a student body of 40K, where Choirs occupy the position of sports at a US Uni , has more than 3 members.