@devilboy
As I was trying to figure out how much this (acoustic treatmernts) would work, I purchased some acoustic absorption panels, and for diffusion, finally chose some architectural 3D/sculpted polymer type 'tiles'. A box of them, approx 18"x18" cost me about $70 for ten (? cannot remember exactly). The are primarily for a 3D architectural surface 'decoration' on walls, etc., and can be painted, which I did for my fireplace opening between the speakers to blend-in the brick surround at the opening. The ones on the walls I just kept unpainted, or white. But, while studying my options, I saw others had used them for audio diffusion purposes as well, so took a shot.
They do work, as there is a difference with and without. As it is also my living room, they are also fairly non-offensive in looks. Are they as good as true purpose built audio diffusion panels? Probably not, no, but they do help and do work. I may consider replacing them with a true audio product in the future, but right now I'm pleased with the results.