You may also want to check out the original Swingle Singers from back in the day: Les Swingers Singers J S Bach Fugue in D Major 1969. It's a short classical piece done a cappela except for jazz drums and bass backing! Pretty astonishing.
I am so excited that someone else has discovered The Swingles {formerly The Swingle Singers founded by John Swingle}. I remember hearing them in late 1960s singing classical music no words. To help you discover them look up their collaboration with your friend Peter Hollens on "Wayfaring Stranger" {I listen to this when I need to calm down or stop worrying}. Note they are British except Sara who is the last soloist from USA. For more beautiful sounds there's Blackbird/I Will one on a church, another a video. Then there is Libertango no words and well acted video. Then there is the Subway video. Look around at their other stuff. Enjoy.
Ward Swingle is the founder. He was an American living in France when he put together a group of session singers in the ‘60s. He arranged music by Bach and gave it a jazz swing. By doing that they won 5 Grammys during those first years as a group. Ward passed away several years ago and was still involved with the group.
I thought the Swingle Singers were discontinued in the 60's! (edit) so after some quick checking, the FRENCH group ended in 72, but a British group was started soon after. It seems that they are a bit like the college based groups or Menudo in that folks age out over time. You do need to hear the Pentatonix version as well.
Merry Christmas Britt.. And to your family. Thank you for another year of making me smile. You have a way about you. Love and Light. P. S. Carol of the Bells is my favorite Christmas song. My Ex BIL is a DJ. And he made me a whole Playlist of just that song by everybody he could find! 🎄🎅🤶🎄