Stock stereo with subs?
 

is it possible to keep the stock stereo deck and still put subs into my car?

Well anything is possible, the question is whether there's a point to it. Sure you can do it, but the quality is only as good as the weakest link in the system...which in this case is the stock deck.

you will need a line converter to turn the left/right rear speaker out line into an rca line
then that and a rma or remote power wire will go to an amplifier from the amp you then hook up the subs i did this to my wifes mazda 3 it works but you wont have rear speakers unless the are ran by an amp too. you will have bass in the back and treble up front no mids.