I asked The Younger Son to pick something for us to listen to during lunch, and he picked something suitable for an SCA Christmas. It's a Phillips CD, recorded in Vienna in October, 1985 and offered by the Musical Heritage Society in 1989. I used to get music regularly from the Musical Heritage Society. I don't see this at their site now.
from the notes included with the cd Gregorian Chant by the Schola of the Hofburgkapelle, Vienna:
This recording includes all the music sung at the third Mass of Christmas with the exception of the Credo. It is framed by the hymns "Christe redemptor" and "A solis ortus"...It includes 2 chants from the Mass for the Feast of the Epiphany.
This recording also offers chants from the days around Christmas, mainly taken from the Propers of Masses.
This CD seems to be the same as this one listed here at Amazon.com. Some of the music can be heard there. The CD is currently available on ebay, which is where I got the photo.