Thank you millercarbon for your kind words.
Gdnrbob made an insightful observation: "...it just makes sense that multiple subs will nullify/even out room nodes. Any of the subs listed would do that, when 4 or more were hooked up."
Yup. That’s why I don’t claim that my four small subs are the one and only way to do it. For example Millercarbon is building his own four-sub system, using a better woofer than the one I use.
And the subs don’t have to be identical either. So you can start with what you have and add on.
Duke