In a rehearsal room perched above the labyrinthine backstage of Florence’s starkly contemporary Maggio Musicale Fiorentino theatre, Luca Guadagnino is showing the women of the chorus how to make a second-act entrance. Dressed in a slouchy cardigan and slacks, the Italian director runs forward and stops short at a line of tape indicating the rim of the stage. A little out of breath, he turns past stretching dancers to conductor Lawrence Renes and asks if he minds the sound of stamping feet. “I never mind when we hear them talk, walk, breathe,” Renes says. “It’s live theatre.” Better known for...