Kyrie ad lib. VI in the Vatican edition is an elaborate melody the mediæval manuscripts assign to the greatest feasts of the liturgical year, especially Easter. It bears a marked musical affinity to the Kyrie I, Lux et origo, the other usual Paschal setting, and Dom Pothier suggested it arose as an embellishment thereto. It is impossible to be certain of this conclusion, however, and in fact the earliest sources for Kyrie ad lib. VI date from the 10th century, whereas the earliest for Kyrie I date from the 11th.
Two roughly contemporary sets of tropes circulate with this Kyrie, both as exuberant as the melody itself. The Western Frankish manuscripts feature the following trope:
We humbly beseech thee, Christ almighty king, that thou mightest deign to have mercy on us.
Thou alone are worthy of praise with ceaseless revel, by which we ask thee singing, have mercy.
O good king who sitteth above the stars, and lord who ruleth all, have mercy.
Thy devout people implore thee ceaselessly that thou thou mightest deign to have mercy on them.
O holy God, our life-giving redeemer, save us, have mercy.
We sing before thee, look favourably on our prayers, and do thou have mercy always.
Our assembly now crieth unceasingly and sayeth, have mercy.
Have mercy on us, son of the living God, have mercy.
Great glory be to God on high, to the eternal Father who redeemed us by his own blood to save us from death, let us all say unendingly together, have mercy.
The Eastern Frankish sources provide a trope with even more Greek elements: Κύριε ὦ θέος, κρίτις δίκαιος ἰσχυρός καὶ ἀθάνατος ὑμᾶς ἐλεῖσον.
Lord God, Just, Mighty and Immortal, have mercy on us.
Loving Father, enthroned above the wings of the Cherubim and Seraphim, look with tenderness and mercy upon the sins of thy servants.
Thou alone art worthy of hymn, melody, song, harmony, and praise (αἴνεσις), the voice of all manner of tongues.
Christ, the Father’s only Son, foster thy nature in us,
For whom thou borest the tree of the Cross (σταυρός), shedding thy blood in a purple gush.
Thou Holy Spirit, deign to mingle in our odes most fittingly;
Who joinest the living and the dying, who createst little man.
Have mercy thou on his weakness by blotting out his offenses.
All together with full voices we praise three, Three and One, whose Godhead livest and reignest together and equal in the Trinity, now, and for endless ages and ages, amen, for aye!