A collaboration between the composer Steven Stucky and the writer-pianist Jeremy Denk based on Charles Rosen's book of the same name, this daffily absurd opera buffa ("of sorts") is the only opera in which Haydn, Mozart and Beethoven meet characters named Tonic, Dominant and Subdominant in a bar. Hilarious and vital, the message is that style must live so that music doesn't die. The Knights play, Robert Spano conducts, and before it all begins Mr. Denk tinkles out a Mozart piano sonata.