Possible Clues:

• Almost insult one composer and another
• A composer frequently, we hear, supported by another
• Composer of 'Orpheus in the Underworld'
• Adopted French composer, frequently said to be a German one
• One composer regularly heard with another
• Fr. operetta composer
• "Orpheus in the Underworld" composer Jacques
• German composer whose style is typified by his 'Orpheus in the Underworld'
• High note penned by every single composer
• Composer on holiday with another, eating nut