Thanks for those links.
I did a lot of quartet and double quartet singing for Christmas in the past. We called them “Rent-A-Carols”; it was how we raised funds to tour Europe and compete there. They included some fancier pieces and arrangements, along with standard SATB carols.
Since it was a high-end ensemble in Silicon Valley, we got lots of gigs. We were hired by Google once for their campus Christmas party, but mostly by smaller companies - technology or business, or private parties for millionaires in their mansions. Always in concert attire, of course.
Balance was always an issue, so there was someone in charge of scheduling the gigs, and making sure each quartet was balanced in terms of voices - blend and volume.
I never sang a piece like this in quartet before, nor have I ever heard it done by one. It sounded better than I would have expected.
Of course, we sometimes would sing such in practice quartets, again for balance, but not in an actual performance.
That was Robert Shaw’s key to his enormous success: He made them sing everything in practice quartets. If they could do that balanced, then the whole choir would be balanced.
(Amazingly, Shaw did not sing himself, and only played some guitar. He was not much of a musician per se, but he created the American choral tradition.)
Anytime you want a video of images made to an audio track of your group, let me know.