fat eddy: Yes ...and no.
The manufacturer has decided that the BANGing is a problem with the boiler and has agreed to replace it. At that point, I asked the installer to double-check if 187MBTUH input is the right size for my 2400 sqft home. He's agreed to install whatever size I think is appropriate. (?!) The mfr will ship whatever we decide on. (Why not? It will most likely be smaller.)
Since several people like yourself suggested that we install 1 circ/zone, I wanted to learn a little bit more about flow rates. (I didn't really get an answer from installer when I asked.) I think what I'm finding-out is that the installer really didn't put much thought into feet of head and/or the circulator.
Naturally, I'm getting a little frustrated. I liked and trusted everyone I worked with at this contractor. Other installers that tried to diagnose the BANG commented on the "good workmanship." But, since I now think the first boiler was mis-sized, and since I'm now finding possible shortcomings in the distribution system, the installer is losing patience with all my questions.