A bit of Bach, a sampling of Strauss, plus an offering of Offenbach. For the first time in over a decade, The New York City Gay Men’s Chorus (NYCGMC) devotes an entire concert to the classics. Under the direction of Casey J. Hayes, the 150-voiced NYCGMC treats its audience to some of the most beautiful choral masterpieces of all time. Kathryn Day, by courtesy of The Metropolitan Opera, is the special guest star.