I was thinking about doing exactly this, glad I found this discussion. After musing over what to do with my setup, I finally concluded that my setup is good enough and a great way to upgrade my system for relatively little coin was to add another AHB2.
My setup is a little different as I am using an 8" single driver sealed box speaker, so the bridged watts are not a need; 100 is enough, so I will keep the duo in stereo mode.