After watching the video posted by @audiokinesis I have to say this mirrors my findings. I have gone down the road with numerous acoustic panels, bass traps, and diffusers. I would say the best I tried were from a long defunct company called Eighth Nerve, and the most effective trap was the triangle placed in the ceiling corners. In my system my DIY DBA made the most significant difference (in a bi-amp or tri-amp set up) and I was able to rid myself of a lot of extra stuff hanging on my walls in the process.
