Possible Clues:

• Operatic offerings
• Beethoven's "Ah! perfido" and others
• 'Madama Butterfly' has four
• Solos in operas
• Solos for opera divas
• Óscar ___, 1987 Peace Nobelist from Costa Rica
• 8 Down solos
• Long solo songs
• Challenging soprano pieces, say
• Solos in 2-Down