General Construction Question: 2nd layer of drywall?

[cinemaphile]

In constructing my home theater, for sound barrier I'm using a second layer of drywall with Green Glue between. When putting up the second layer of drywall, am I trying to secure it all the way through to the ceiling joists/wall frames, or am I just securing it to the first layer of drywall? I ask because the screws I've been using (1 1/4") would barely be touching the wall after going through two 1/2" sheets of drywall.