1/2" Celotex instead of sheetrock in sound room?

I am about half way through building my sound room, I have finished the first floor and the garage part. I am about to start on the walls of the room itself. I was planning on using 2 layers of sheetrock for sound isolation properties, when someone suggested substituting one layer of "Celotex", a foam type insulation board with an aluminum foil wrap. Since I live in cold clime, it would certainly help with insulation, but will it adequately work with the sheetrock?
Sandwich two layers of sheetrock an either side of the Celotex. This gives you a high, low, high mass property and serves as very good isolation. It is not as good as using resilient channels, but short of that method of construction it works very well.
You should make the side walls with a slight taper this will cut down on the nearfeild reflections.

I read this in Stereophile right after I built my sound room.
Glue the celotex between the studs. Blow insulation in the studs and put two layers of sheetrock on the walls and ceiling. Put rubber strips on the ceiling prefering using perpendicular firing strips. Put a layer of 1/4 to 1/2 inch cork on subfloor and apply second subfloor over it.