I've heard it said that "In splendoribus" is one of the most beloved of the entire Gregorian repertoire. Its calm, steady, ominous sound, so clean and clear in its simplicity, heard during the first communion after the birth of Christ, provides a revealing melody for the text: "Amidst the splendors of the heavenly sanctuary, from the womb, before the morning star, I have begotten you."
Here is a recording of the Antiphon with Psalms, sung by chant master Scott Turkington using his new Roland R-09. And here is a beautiful edition prepared by Richard Rice.