Which component is most responsible?

I appreciate all of your responses thus far. I'm beginning to think the weakest link is my speakers. I recently went from a solid state amp to a pp tube amp that opened the soundstage and provides a tonality in ways that it will be very hard to go back to a SS amp. However, I think my Polk LSI15’s are limiting me in achieving distinct separation of voices in a chorus. My front end consist of an Oppo with a Monarchy MN24 DAC, which is a very organic. I alternate between the internal Preamp in the Monarchy and a passive preamp. I don’t think the electronics and source are the culprits??

FWIW, separation of voices in a chorus is very difficult to achieve UNLESS it is in the recording in the first place! And it usually isn't, at least in my experience. Be sure you have a recording that really has the distinct separation of voices you are seeking. The clarity that you seek would also be apparent in the 'soundstage' presented by an abundance of recordings and would not only be apparent in the separation of instruments. That is just a starting point. Once again it is clarity of individual tone as well as location of the instruments.

I can not comment on the performance of your Polks. I've never heard them, but that said before I decided to ditch them I would be sure I had them, and my room, optimally set up so I could tell if they really were deficient or if it was just premature up-gradeitis.

Newbee, perhaps you could suggest a suitable recording to the OP that you know has a good separation of voices. That takes the recording variable out of the problem.

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.

Yes, you need a good choral recording recorded a certain way to even have a chance, so make sure that is in place first, otherwise you will spin your wheels.

Here's a good recording to try off the cuff:

Mitch Miller

Here's another:

MTC