Thanks for moving this to the public forum. 
My only two options would be to suspend it from the ceiling near the back wall or place leg supports and again position it up near the wall.
I imagine either of those will be fine.
My concern is will this three or four inch gap between the rear wall and the diffuser cause unwanted resonance?
Probably not, since it's not a sealed cavity. But you could always stuff some fiberglass or acoustic foam in there just to be sure.
My next question is bigger better than smaller or vica versa? I was contemplating using one sheet of 4x8 birch wood and make one large diffuser.
Yes, that's what I'd do. A small diffusor on a large wall is not so useful - acoustic treatment is about percentage of surface coverage.
--Ethan
to the ears any more. As a matter of fact my wife who is down stairs says it sounds better to her while she sits down stairs watching television (she is happy listening to a boom box) for it doesn't irritate her any more ( for her to comment that it sounds different/better especially from downstairs say quite a bit).No more "ringing" and the depth in my small room doesn't so small acoustically. My wells are about 5 inches deep and I am sitting about five feet from the diffuser. The diffuser is 4x4' and has significant weight for it two people to transport it up to my music room. I am impressed and pleased as to how well it truly works. Thank you so much for all of your advice. I am going to take some time off by not working on my music room and enjoy it. Again much thanks! 
