Suggest you forget the drywall ceiling, and use acoustical tiles, which are not called acoustical for nothing. I used Roxul bats, and Celotex tiles that are 2x4' but made with a groove to look like 2x2'. One three inch Roxul bat is plenty. Use lengths of steel wire cut an eighth of an inch longer than the distance between joists to hold the Roxul up against the floor. Leave an airspace between the Roxul and Celotex. Avoid flourescent (sp?) lights; use recessed lights instead. There's a rule or formula for spacing recessed lights to prevent shadows on the walls. I used this approach. It has many benefits. e.g., sound doesn't travel to the main floor; ceiling is practically transparent acoustically for good vertical soundstaging; combination of bats, airspace, tiles, grid, joists, and lighting make for good absorption and diffusion; and it's easy to remove tiles if needed for pipe, electrical, heating, etc., repairs.
Good luck
Jay
Good luck
Jay