The most interesting book about music I read was "Mozart, Sociology of a
Genius", but this is the title in Portuguese (I am Brazilian), and I am not
sure it's the original title in English.  The author is no one less than
Norbert Elias.

The biography of Beethoven by Maynard Salomon is great, too.

And very nice is the book is "The Loser" Thomas Bernhard, about Glenn
Gould.  (Phoenix Fiction Series Jack Dawson (Translator) / Paperback /
Published 1996)

Good Times,
Renato Vinicius