Recently went dual F12s - totally recommended

I can't really suggest the physics of when to do it or not, but I figured I should say if anyone is on the fence, Rhythmic stuff is insanely good and the leap from single sub to dual was pretty well worth it for me if anybody is on the fence and has the amps on the circuit to spare.

There's the "sound isn't as localized thing" but there are certain movies or episodes that don't just do the "boom" thing but generate like extremely long rumbles or drones, and those are just my favorite. Bass is also especially nice and tight and not like the typical distorted sine waves of the usual subwooferness. Usually doesn't shake the house or hit you in the chest (unported here, so...) but if it hits the right resonance it totally can quite impressively.

I previously had a single SVS-2000 before they added the new DSP version, and I think it's a HUGE step up. Still like SVS, nice people to talk to.

I was able to keep the main AV system on a different circuit as the subs and made it out ok, the servos are nice as they are less watts than some other options and take less power to do nice things.

Anyhow, yeah, dual subs are nice!