It seems from reading many threads on Audiogon that outboard sub implementation is always frought with problems. Why not consider purchasing a pair of real full range speakers if you feel that last half octave is worthwhile? Rives has demonstrated that your speakers can reproduce below 30 hz. If you are in fact getting all of that now, there isn't much you are missing. Perhaps you need to consider whether or not your room is delivering all of what the WP-7 provides.
I have equalized bass from a full range speaker with audible signal below 20 hz. If I cut it off at 30 hz, I experience insignificant loss.
I have equalized bass from a full range speaker with audible signal below 20 hz. If I cut it off at 30 hz, I experience insignificant loss.