Five acts or four? Italian or French? Beyond top-level executive decisions in mounting Verdi’s Don Carlo(s) lie plenty more. Surely the very last thing the score needs is extra music from an alien hand. Yet for this festival premiere of an Italian edition in four acts, the German maestro Christian Thielemann (a sometime Verdian not without his admirers) has ordered up a new “instrumental prologue” from his prolific, professorial compatriot Manfred Trojahn. Once that’s out of the way, a fancy cast takes over, led by Ildar Abdrazakov as Philip II, Yusif Eyvazov as his Byronic son Don Carlo, and Anja Harteros as Elisabetta di Valois, torn between them. —M.G.