Bob Mondello quotes:

The psychological detective story in "Equus" made Peter Shaffer's name as a playwright. But it was his next play, "Amadeus," that cemented his reputation, largely because of the movie version. Another battle of wills, it was the story of composer Wolfgang Amadeus Mozart seen through the eyes of lesser composer Antonio Salieri.

I mean, the paradox is that whereas the screen, it seems to me - the cinema can absorb endless amounts of music, it cannot really with comfort absorb large amounts of words. Not nearly as many words, that is to say, as a stage can.

The music is not used repetitiously to create film atmosphere. It is, in fact, the leading character.

That it might turn into music that would heighten emotion, but not be important in itself.