Tchaikovsky’s “Iolanta” and Bartók’s “Bluebeard’s Castle” will return to the Metropolitan Opera as a double after a successful run a few seasons ago. On first look, it seems like a strange combination with the composers’ styles rather different overall. It takes a truly strong maestro to move from Tchaikovsky’s lush lyrical qualities to Bartók’s challenging harmonic structures. Hungarian maestro Henrik {…}