Luthien begins to sing and dance, turning Sauron’s music into something harmonious. Daeron and later Maglor join in.
A misreading of this line on my part led me to a fun idea: "turning Sauron's music into something humourous". What if her pushback against dreary Sauron is to make everyone laugh? Some sort of proto-Tra-la-la-lally?