It is not possible for music to exist necessarily, and I would venture to say that Aref knows that. He was simply trying to illustrate that the greatness of the music does not increase simply because it is necessary. And if its necessary existence cannot make the music any greater than if it has contingent existence, then necessary existence is not a great making property, and the ontological argument fails.
I actually posted this topic under the ontological argument as well. If I don't get much response there either, I will post it under the general tab.