Solution to 4: Listen Closely

Each piece has a specific composer; the first letter of each last name spells out MODEST:
Mozart, Offenbach, Debussy, Einaudi, Saint-Seans, Tchaikovsky
However, Modest is a first name, while all of these are surnames; if Questers guessed Modest, they would receive the clue “Who’s that?” 
This, coupled with the subtle clue of “sure name” (surname) in the puzzle description suggests to use a last name, so the answer is the composer with the first name Modest.
MUSSORGSKY