Think of drywall as another bass panel...it shakes.
If the room is mainly for sound, consider studs every 12 inches instead of 16", screw and glue 1/2" plywood up first, then put drywall over that with screws and glue. Even using double sheets of drywall will help.
Secondly, decouple the walls from the ceiling above. Putting in a false ceiling will both prevent you from hearing above as well as you shaking the upstairs too badly. You asked, this is an expensive way to do it.
Last suggestion, run all the extra wire you may ever want first. I always pull an extra run of Cat-5 to every outlet just for future use. The cost of the wire is minimal vs having an electrician later.