A deeper more holographic soundstage.

I was wondering by what means you have created a deeper soundstage. I am satisfied with the width but I really feel it is a bit 2 dimensional. It doesn't go back far enough. I like more layers of sound that reach towards you from the blackness.
As I've already spent quite a bit on my system I am unable to buy much more expensive components.
Did you upgrade one component that made the difference? Placement of speakers? New footers or tweaks such as Stillpoints?
Two subs instead of one(I have one)? Different placement of subs? I am working with a very tight space so it is difficult to move things without them being in the center of the room.
Any suggestions would be greatly appreciated.