I finally got time to find a contractor who would demolish a wall and install a new soundproofed wall. Interestingly, the previous owners actually had not 1, but 4 layers of drywall. Between each layer was nothing like Green Glue or any compound, just an extra layer of drywall with some sound board. In addition, there was already R-13 Fiberglass insulation. Four layers of drywall, a layer of sound board, R-13 insulation, and nothing in between the drywall still sounded terrible. Who knew! In case you're bored and never saw a wall destroyed, (like me!), it's a pretty interesting look into how buildings are made.
Soon, a new sound proofed wall.. soon.