Recall that below tune in a ported sub is mostly distortion.
You sure you want that?
That black graph looks awesome to me and if I owned the 215HT I'd do exactly that 20hz, 48db/octave hpf and crank the snot out of those speakers without ever having to worry about bottoming out drivers. Except I'd use a dsp 6000. 2000 watts per channel is about perfect.