[jmil1974]

Custom, I would avoid the 6x9s behind or under the seat. You'll lose a ton of sound, through your legs or the seat. Do the door bit and slap some sound deadener in there and you'll be surprised.

Go for a 4 channel, hook the 6x9s up to the front channels and bridge (combine) the rear 2 for the sub. The EQ I mentioned has a built in crossover, to send the right frequencies to the right speakers, as well as fine tone control. If you have the stock seat, there is room for a 10. Stick with one to make sure you have enough air space.