There was once a page with the lyrics, but it seems to be gone now. You might be able to find lyrics to some of the hymns on this site, though, as that link demonstrates.
This kind of thing is what I'm most interested in, though: a "troped lesson (mp3)." I'm pretty sure it's Laudes Deo, about which this site says:
The troped lesson Laudes Deo for two voices, sung at Midnight Mass of Christmas, is essentially a display piece for two solo voices: with its elaborate melodic writing and even more complex rhythmic effects, recalling the music of the Eton Choirbook composers and of Johnson's fellow-Scot, Robert Carver, it probably dates from about the same period. Only selected passages of this text were set in polyphony, the intervening ones being sung in plainsong. These latter have been supplied from Sarum missals and are marked with square brackets in the text below.
Will be checking this out on the web to see what I can find - and I'll come back to post the words if I find them. It's gorgeous.
[EDIT: Apparently Laudes Deo starts out this way:
Laudes Deo dicam per secula
Qui me plasmavit in manu dextera
Et reformavit cruce purpurea.
And apparently, it was "the most widely known farsed Epistle" and "was sung all over Europe on Christmas Eve, Christmas Day, or Circumcision."
("Farsed"? From the same source:
A different way of elaborating chants on special feasts was employed from the twelfth century onward for lessons and some other chants, especially in the highly individual liturgies of such feasts as Circumcision known from Beauvais, Sens, Laon, and other centres (see above, I.9). Phrases of pre-existent chants were inserted into the lesson. Such an insertion is often referred to as farsa, both in the Middle Ages and modern writings, although "farse" can refer to other types of troping as well. The epistle of [the] mass was the chant most often farsed: over forty examples are known (nearly all listed, with sources, and with the epistle tone the accompany, in Stablein, "Epistel", MGG; see also Huglo, "Epistle", NG). The Gospel, by contrast, was left unadorned (Stablein, "Evangelium", MGG cites three examples only, all found in German and Swiss sources). The Paternoster, Nicene creed, and (from Compline), the Apostles' Creed were also farsed.
"Tropes" will be the topic of the next lesson, as we back up from here.)
And apparently Laudes Deo continues this way:
See what you can find out at Google Books these days? I wonder if at some point I'll be able to get all the words? I bet so!]
[EDIT II: Derek helps out again! He gives me this English translation:
May I speak forever the praises of God,
Who formed me in his right hand
And reformed me upon the crimson cross.
A birth by blood which all redeems
From the rising of the sun's orb through the climes
Until the world's westernmost parts
In praise of whom let shouts ring out.
And here is a (too-short!) clip labeled only "Sequence". It sounds a lot like parts of Lauda Sion Salvatorum, the Sequence for Corpus Christi! In any case, it doesn't seem to be the Sequence Hymn for Christmas Day, Letabundus, which is also prescribed by Hymn melodies for the whole year from the Sarum service-books for Second Vespers of the Feast of St. Mary the Virgin on August 15:
But maybe I'm wrong. I certainly need to know more!
[EDIT: Our good friend Derek stopped by to offer this, in re: the Sequence:
The Burgundian Cadence page says that this is "the 'Cockcrow Mass'".
There are three masses traditionally said on Christmas that correspond to three stational churches in Rome where the pope had to go and celebrate festal masses. Once these left Rome they got to be known by the time of day when they were said rather than the station church names (the old way of referring to them). The mass they're referring to is the "Missa in gallicantu."
And then he notes that "....the sequence for the Sarum Missa in gallicantu is Nato canunt omnia...." - educational, as always, and correct! This is indeed that Sequence. This Google Books entry has some of the words, to wit:
1. Nato canunt omnia
Domino pie agmina
2. Sillibatim neumata
3. Haec dies sacrata
In qua noua sunt gaudia
Mundo pleni dedita....
You can see what might be all the words on page 10 of this PDF file; it's a musical program, and one of the pieces performed is a version of Nato canunt omnia written in the 15th C. by Antoine Brumel. The English translation is there along with the Latin; I'll try to find this elsewhere also (it's difficult to copy from PDF content, or I'd put it here right now).
Thanks again, Derek!]
[EDIT II: Ah! Found the lyrics to the Burgundian Cadence clips! They are all here, and the words, plus translation, to Nato canunt omnia are these:
Nato canunt omnia Domino pie agmina,
Haec dies sacrata in qua nova sunt gaudia mundo plene edita;
Hac nocte precelsa intonuit et gloria in voce angelica
Fulserunt et immania nocte media pastoribus lumina
Dum foventsua pecora subito diva percipiunt monita:
Natus alma virgine qui extat ante saecula.
Est immensa in caelo gloria pax et in terra.
Hinc ergo caeli caterva altissima iubilat
Et canto canore tremat
Alta poli machina;
Sonet et per omnia hac in die gloria voce clara reddita.
Humana concrepunt cuncta Deum natum in terra.
Confracta sunt imperia hostis crudelissima.
Pax in terra reddita nunc laetentu omnia
Nati per exordia,
Solus qui tuetur omnia
Solus qui condidit omnia;
Ipse sua pietate salvat omnia peccata nostra.
Let rank upon rank now dutifully sing to their new-born Lord,
with music of instruments fitted to their words.
This is that holy day on which new joy is
Proclaimed to the whole world;
And on this night angel voices have sounded "Glory in the highest."
And in the dark night a great light has shone upon the shepherds.
While they tended their flocks, suddenly they heard the heavenly message;
He is born of a gentle virgin, he who was before time
Great is the glory in heaven, and great the peace on earth.
Now the high host of heaven exult therefore
And at so great a sound the lofty vault of the sky trembles;
And the glory proclaimed on this day resounds everywhere.
All men sing out together of God born on the earth
Shattered is the cruel empire of the enemy
Let all rejoice to see peace restored to earth by the birth of this child
who alone watches over all things,
who alone created all things:
For he by his obedience takes away our sins.]