I am in the process of building a theater room in my basement. My room is about 13 by 22 feet, and I want to build a viewing platform at one end of the room. Is it best to use 2x6's for joists or will this make it too high, and should I use 3/4" plywood or MDF for the top? I am also debating if I should fill the platform with sand, or if insulation will be good enough. I am probably going to put my subwoofers in each corner of the platfrom, and am concerned about the bass being affected. Any ideas or suggestions would be appreciated.