another good recommendation besides insulation is sound deadening board (if you can't find this at your hardware store then use builder's board). It costs less than $7.00 for a 4'x 8' piece, plenty for all theater speakers. just cut it up with a utility knife and screw it in with screws inside the cavity. then fill the rest with insulation. Not only will it lessen the sound going up to the second floor,but it will also increase your mid-bass tremendously. I personally like Polk Audio RC80i 8" in-ceiling speakers with pivoting tweeters. great for invisible home theater use.