Tom,
I stay away from QuietRock due to the cost and hassle. You can do better with other materials and methods. That kind of mass is mainly going to help with sound transmission between adjacent spaces, not improve your reverberation times or room modes in the listening space.
You should always measure and adjust to get controlled and linear RT times. Depending on the room size, for critical listening spaces I want the reverberation times to fall between 0.25 – 0.4 seconds from 125Hz. and up, with a slightly ascending decay from 125Hz. and down to about 0.7 seconds. It’s all about the right treatments, in the right locations, and the right quantities.