Not an answer, but another question. I have the same concerns. I am committed to using can lights in my basement ceiling. I have 21 already installed in my basement (IC rated). I will be using RC and fiberglass insulation for the ceiling. I am considering using sound board (for $9 per 8'x4' board), or Mass loaded vinyl (at least $2/sq. ft. with shipping), or nothing extra under the studs. My real concern is the can lights. I don't want to waste money on a pricy soundproofed ceiling if it will mostly be lost through the can lights. I am considering wrapping the can lights with several layers of Mass Loaded Vinyl to make a quick and easy sound box around the already installed can lights. I have searched several forums and have never heard of anyone else having tried this. Has anyone done it? Is it safe (the can lights are rated for contact with insulation)? I'm sure it would help some, but how much? Enough to justify using more than just RC and insulation with 5/8" drywall?