(Photo credit: Monika Rittershaus) Who’s afraid of a double bill? Part two. If Gluck’s Iphigénies required stamina from Aix operagoers, the double bill of Peter Maxwell Davies’s “Eight Songs for a Mad King” and György Kurtág’s “Kafka-Fragments” beseech us to be attentive. It was just an hour and a half of music, and the performances were vivid. But the musical {…}