I've mentioned in previous threads that this was exactly what my dream had always been in car audio. Build a sub box with a 15 or 18, a 12 and an 8 or 10 inch woofers all pushing different frequencies. I'd be very surprised if to date nobody has every tried it. Although I have yet to hear about it if they did.

My Stuff :

M80's
QS8's
VP150
EP800
Denon 4802
Emotiva XPA-3
Samsung BD-P3600
Sharp 65 Inch Aquos LCD