[morgal48]

IIRC the factory amp has a low pass filter that chops signals above a very low frequency - maybe 50Hz. Using either factory Haes 4X40 or 6X40 amp you'll not get any frequencies above that from any subwoofer. BUT, if you replace the Haes amp with about any other 5 channnel amp you can adjust the bass response. Using the factory 2-ohm door subwoofers, wiring the doors in series (impedance drops to 1-ohm), the bass response can be adjusted to a level that bass is all you hear, and feel. Two 5-1/4 in. speakers have more surface area than one 10 in. speaker, and push more air - through a speaker system designed by guys who design speaker systems for a living.