Possible Clues:

• Cos¿ fan tutte and The Magic Flute
• "Fidelio" and "Orfeo ed Euridice"
• La Scala performances
• Son on piano in old-time musical performances
• Productions that showcase 15-Across
• 'La Boheme and La Traviata, say (6)'
• Shows at the Met
• Gluck works
• Times of work for such as car men
• The music's played as they're played