Dear Jarrod,
As for a reliable text, there is the critical edition by Durgamohan Bhattacharyya, Chāndogyabrāhmaṇa, with the commentaries of Guṇaviṣṇu and Sāyaṇa. It was published as Calcutta Sanskrit College Research Series, no. 1, in 1958. It is based on four printed editions and eleven manuscripts.
An English translation by Sakuntala Rao Sastri was published as The Mantra-
Brahmana (A book describing the earliest domestic rituals of Aryans), by the Viswa Parishad, Sanskrit University - Japan, no date. It is a typescript.
Upon checking OCLC for more recent publications, I now see that Sakuntala Rao Sastri has also published a romanized critical edition of the Mantra-Brahmana, but I have not seen this book.
There is an early Sanskrit edition that includes German translation in two publications, one for each of its two prapāṭhakas: Das Mantrabrāhmaṇa. 1. Prapāṭhaka, by Heinrich Stönner, Halle: 1901.
Das Mantrabrāhmaṇa. 2. Prapāṭhaka, by Hans Jörgensen, Darmstadt: 1911.
If you cannot easily access these books, I can scan my copies.
Best regards,
David Reigle
Colorado, U.S.A.