From what I could find on the Vox Domini chant, it seems it is not an antiphon originally, but a second mode verse for Epiphany. See F-Pn lat. 15181, 163v (Bréviaire de Paris, c. 1300). I transcribed the chant, as it appears in this source (and changed the last word 'maris' to 'multas', to match the text from the Roman Pontifical):
In the source, the text continues with 'paterna', but I suspect this is the start of something new and not a part of our chant. Please correct me if I'm wrong, or if the end of this antiphon sounds strange.
The antiphon Deus in sancto via is found in the Psalterium Monasticum, 177:
Here it is; one would have to look up either a medieval Pontificale manuscript or a 20th century Pontificale print with musical notation to get a non Medicae-ised version.
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