Wow Cap'n Rick.
Your duet knowledge certainly spans the years
Needed Wednesday Nudge 1 and had to google the Usher crosses - ya never know these days.
Were you sacrificing rabbits by including twosomes in clues, i.e Adam & Eve, Keats/Shelley, Jane Fonda/Jon Voigt, Almond or Cashew, Univ. or Acad.? First letters of those answers to those + DUETS33DSongs for 51-Across[-----] gets you SECOND; Almost made it to SECOND BASE.
Love duets but quartets are great too - the 4 TTOPS54ASporty car roofs[-----] especially.
As always, thanks for the MMM!