Whart,
I contracted Nyal Mellor of "Acoustic Frontiers" to design the whole room, including construction specs, electric, etc.
Initially I was thinking of installing a second layer of drywall on a top of the old one, with Green Glue in b/w the layers, but Nyal thinks, that a single layer of 5/8' damped drywall is a better option.
So, here I am, removing the old drywall.
Actually, I'm glad I did- first, after exposing the walls and the ceiling, my contractor discovered a leak from the toilet above, two disconnected air ducts and some other small problems, previously hidden under the drywall.
Also, the electrician's job of installing dedicated lines will be much easier (and cheaper), and I can better supervise it.