i had a boss audio camp (CH-450 i think) amp under my drivers seat for awhile.. that put out 50x4.. it wasnt the best amp in the world but it did the job and sounded pretty good.. plus it fit under the seat.. ive since upgraded to a larger amp that just sits behind the drivers seat for now

like i said.. i've got 2 rockford fosgate 8's run parallel off a 300x1 @ 2ohms sub channel on my amp and they hit hard

did you try upgrading all the wiring? the stock wiring isnt going to carry a very good signal.. i ran 12ga to all my speakers when installing the new amp