I too am about to do some acoustic treatment in my new listening room. I was recently recording at a friend's studio that has a fantastically treated, shoe-box shaped recording/mixing/mastering room. Always envious when I walk in there, I asked him for some advice on how to get similar results.
His first suggestion was to avoid the typical pyramid foam, and instead build/buy multi-layer absorption panels with rigid fiberglass, and covered in burlap-like fabric. For him these yielded a much larger improvement. He said to place them at the first reflection points on the side walls. These are found by sitting in the listening position and having a friend run a mirror along the wall until you are staring directly at the drivers of the respective speaker, mark that spot on the wall as first reflection points. Also make sure you have absorption panels on the ceiling above the listening position and on the wall behind it. He has panels hanging from chains in the ceiling corners to eliminate 90 degree angle's negative effect on sound. This room is carpeted, with no windows and a curved rear wall. It looks like its bowing out almost. I forget what the purpose of this is, but I think it has to do with bass freq. He frequently claps and listens for echo too.
Since each room, equip, and listener's expectations are different, I'm sure you will have to modify to get exactly what you want. Good luck! Keep us updated with what works for you
