i would not get full range speakers because the amp is low pass only there are some companys that make 6x9 subs but they will defenitly need more power that amp that is back there is only like 50 watts RMS maybe 150 max the best option if you dont want to add a real sub box, is to moddify your stock enclosure. in my first ls before i put in 2 15" L7's , i took the stocks out and plugged one of the holes with 3/8 mdf 6x9 cut out and opened the other side out to accept an 8 inch L7 and found a new amp (rockford 300 watt RMS mono) that actualy fit in the stock location. i did have to run new power wire from the batt (i know, REAL FAR), ground it, and run a turn on wire since ford uses a 6 volt turn on and the aftermarket uses 12v, however there are low voltage relay that you can get to use the same turn on. and get some cheap rca's, cut them in half, and solder them on to the signal wires at the fact connector, the end result was incredable, everything looked stock and took up no trunk space. and it poundedloud and clean, if you have not heard an 8" L7 it hit as hard as some pair of 12's do. yes it is alot of work but the results pay off, and it only took a little over half a day to complete
