Nice thought, Frizio. I like your solution of covering the back of the head with a sela, to indicate that it's more about music than about these people.
I am afraid that in practice, all 28 member states would want to have "their" national composer on the coin and the Germans and Austrians could rightly claim that they need more than one. The omission of Mozart would doubtless lead to AUxit while I doubt you would want to hear the music of the best Dutch composer.

Music is supposed to unite, not divide. How about a single piece devoted to music without the composers? It's a bit of a challenge, but it can be done.
Peter