The Taittiriya Upanishad ends with a description of what souls do after they've attained Moksha:
He who knows this, when he has departed this world, after reaching and comprehending the Self which consists of food, the Self which consists of breath, the Self which consists of mind, the Self which consists of understanding, the Self which consists of bliss, enters and takes possession of these worlds, and having as much food as he likes, and assuming as many forms as he likes, he sits down singing this Sâman (of Brahman): "Hâvu, hâvu, hâvu! I am food (object), I am food, I am food! I am the eater of food (subject), I am the eater of food, I am the eater of food! I am the poet (who joins the two together), I am the poet, I am the poet! I am the first-born of the Right (rita). Before the Devas I was in the centre of all that is immortal. He who gives me away, he alone preserves me: him who eats food, I eat as food. I overcome the whole world, I, endowed with golden light."
For those who don't know, Saman is a term generally used to refer to hymns of the Sama Veda, so I asked this question to find out where in the Sama Veda this quote from. In this answer, I traced it back to verse 594 of the Sama Veda Samhita:
ahamasmi prathamajā ṛtasya pūrvaṃ devebhyo amṛtasya nāma |
yo mā dadāti sa idevamāvadahamannamannamadantamadmi ||
I have been created before the creation of devtas and nobody can survive without consuming me. Those who donate me in Yagna etc., I protect them and bestow them with the result of pious deeds [punya].
The Samaveda involves the recital of Vedic verses in the form of songs, and in particular this verse has been turned into a song known as Purushagati, AKA Svargyam Sethushama. You can listen to the hymn here (taken from this web page and converted to mp3 format); I highly recommend it if you haven't Sama Veda singing before.
According to this web page and this web page, the hymn is apparently sung by the gods to worship Vishnu in his divine abode of Vaikuntha. But I'm interested in its Earthly use. Pretty much all the hymns of the Vedas were meant to be chanted in some capacity in Yagnas, or Vedic fire rituals. So my question is, how was the Sama Veda hymn Purushagati used in Yagnas?
The texts that explain how to use Vedic hymns in Yagnas are the Brahmanas of the Vedas, which are like commentaries on the Samhitas, and the main Brahmana corresponding to the Sama Veda Samhitas is the Panchavimsha Brahmana, AKA the Tandya Mahabrahmana, associated with the sage Tandya. You can read it here; it's rather long, so it's hard to find the answer. Does anyone know if this hymn is mentioned in there?