What is fascinating about Wayne Marshall is that despite his beginnings in more orthodox rep, this British-born, British-trained artist has primarily made his name as a supreme interpreter of American music. Ravinia will hear him on August 3 in a suite from Porgy as well as in the music of Leonard Bernstein and Stephen Sondheim. “For me,” Marshall explains, “your American music is just as important as any Beethoven, or Haydn, or Mozart, or Brahms, or whatever. It’s the same to me. It’s not to be taken lightly. Porgy and Bess is a phenomenally difficult score. Yes, Gershwin wrote some light stuff, but some very serious stuff as well. And the music is not easy.”