"I've noticed that audiophiles and reviewers seldom write about choral
music. Is it because they don't like choral music, or is it because it
is just really difficult to record choirs well, therefore making choral
music a poor choice to show off a system?"
I've noticed that too Paul and I personally believe that it is often for the reason you note above and others in their responses. I too love choral music and have focused my attention, along with large scale orchestral music around my system in making this type of music as natural and realistic as possible.Agree with Rcprince's observation about vocals, particularly lyric soprano voice can often come through with glare and IMO is about the hardest instrument to sound completely natural through an audio system. I too notice that vinyl recordings seem a bit more forgiving than do digital. I think your remedy could be some or many of the excellent recommendations given above along with seeking out quality recordings. I find close miked recordings of vocals seem more problematic. Getting it right with this type of music has been in my experience "a long road" but your 20 year old impressions concerning a Conrad Johnson preamp certainly is a good choice for this type of music IME.
Agree with Rcprince on the Telarc/Shaw recordings, less notable glare and more of a mid-hall presentation which is ok by me if the recording is rendered more listenable. It seems the biggest problem is the transducers themselves, microphones and speakers at least that is my suspicion. On a final note most of the audiophiles I know don't particularly care for choral music with a few exceptions. I would think that anyone that would commit to purchasing a very expensive pair of loudspeakers would be really committed to attempt recreating large scale music and voice as realistically as possible or what's the point, listening to Rebecca Pidgeon singing "Spanish Harlem" as realistically as possible?