all the guys above know their shit man, y ur not takin it in is beyond me.
firstly u will get nuthin out of ur 6*9's if u shove em behind ur ass. wats the point of putin them there. think!!! spkr dun sound good wen u smother them, thats whats gonna happen if u chuck under ur seats, the cusion in the seat will actually absorb the sound n u'll get nuthin.
chuck dem on the shelf, straight on or box doesnt matter as long as u mount them n make them tight fit. plus dun worry bout low end high end
mine cost me 800 i've got 2 12" subs 800w amp, pioneer deck n 4" n i pulled 132dBz at a recent sound meet. money value is nuthin today
jus build it up peice by peice, dun go blow all ur money in one go, shop around
u should be able to find a decent 800w amp for around the 250 mark i paid 180
n i replaced the factory 4" with pioneer 80w improveed the sound n my limits drastically
n mate a serious atitude towards ur car may need to be in the mail, cos ur gonna need it if u wanna suceed