Full headcanon:
Despite their nature as beyond our plane of comprehension, the Great Ones enjoy human music.
Mergo obviously loves his music box lullaby, as does his Wet Nurse. If Ebrietas had ascended, she would be fond of piano pieces like etudes or concertos, but instead weaves her own mournful melody. Kos enjoyed the working songs of the Fishing Hamlet. The Moon Presence adores the Doll's rare lullaby. If the Brain of Mensis is capable of hearing, it would be fond of string ensembles or solo violin pieces. The Amygdala are attached to different types of music depending on where they lurk, but are generally open to anything. And Oedon loves the human voice, strong vocal solos and opera.
In a kinder world, the Orphan of Kos would have been born and raised surrounded by their mother's voice, echoing the Hamlet's songs of old or an unknowable lullaby born from Kos' own nature...