2 medium sub or 1 big sub???

[nightflier]

I was thinking of getting a second one so I could lower the gain a little and "divide the load" on 2 subs.

So if a less expensive sub was capable of getting down to 30 Hz. and your more expensive sub all the way down to 20 Hz. at sustained decibel levels, how would these be physically connected? And how would you "divide" the load?

I can understand how two identical subs would work in a typical HT setup, but wouldn't different subs create some directionality to the low frequency sounds, particularly for the 30Hz.+ sub? How would you direct the proper frequency ranges to the desired sub?