Inherited a screw up so now what? Please help!

I have been asked to make a control room and recording room out of a previous design and contruction someone esle did before me. THey used dry wall on the inside of the frame. THe owner won't let me take the wall frames out and redue them without the inner drywall to increase the space. So what would make the best outer leaf to go inside the studio? I was thinking resiliant channel - 5/8 dry wall - Green glue - 5/8 drywall. Would that even help? Or should I insist on tearing down the inner frame, getting rid of the inner drywall of the outer frame and building a new inner frame with a 2" air gap between frames?

post a sketch of what you have actually - I can't picture it.......... Rod