I am getting closer and closer to being able to start my theater, I'm thinking a Jan 2nd start date. *fistpump* As I go through this build process in my mind, I'm always coming up with questions.

One question I had was if it would be feasible to have a base layer of plywood for speaker mounting and/or PJ mounting. The plywood would pretty much be applied in selected areas and the 1st layer of rock would be cut around it. Then the 2nd layer of rock + GG would be applied as normal. The idea behind this is to provide a firmer base to install equipment, as well provide some mounting options. This is also coming about since I framed with metal studs.

Any thoughts on this? I was going to caulk around the sheetrock/plywood transition for acoustical integrity, so is there any other things I should watch for?

In my ceiling, I used a layer of 5/8" plywood, GG, 5/8" drywall. I did this to provide a continuous mounting surface for the soffits. Could be a compromise in the long run, but I felt it was worth the convenience. My theater designer didn't totally object.

You did say you framed up the walls in steel. There are several options for you. In your wall cavity, one side of the steel has a leg that faces the other side that is flat...what you could do is go back to your stud supplier and ask him for some backing...they might sell a couple of versions, one I know of is made by Dietrich Metals...it sits inside the cavity and one side is fastened to the lip of the stud...the other side is loose...then you can apply your two layers of 5/8" and go with either green glue or supress DIY adhesive (a little cheaper)....buying the pre-cut backer can be a little expensive...but it saves time...another option is to bo to your local home depot/lowes/menards and buy a sheet of 3/4" plywood (3/4" is a must)---cut strips of either 16 or 24" wide first (you could also make the plywood as long as you would like...from a full 8' x 16 or 24" to as small as 6" x 16 or 24"...then on one side only you would groove out a 1/4" deep cavity about 1/2" in from the side...then place the sheet inside the cavity with the groove accepting the lip of the steel stud and attached through the lip into the wood...when you apply your first layer of drywall you could add a screw or two on the opposite end to better hold it in place for attaching your speakers later.