Hans Werner Henze’s fifth opera, The Bassarids (those who wear fox skins) had its world premiere at Salzburg’s Grosses Festspielhaus in 1966. Now, 52 years later Henze’s massive “opera seria” returns, but to the Felsenreitschule —the old riding school made into a theater that hosts the Salzburg Festival’s difficult operas, the Grosses Festspielhaus now dedicated to the grand repertoire.