This is a pretty good, decently hard hitting system for your sub stage. A q-logic 12" ported prefab box, alpine type r 12", alpine mrp-m405, and it really has a small footprint.
Do you have the monsoon system? If so, you can replace the 4x6's, 6x9's and 5 1/4's in the doors and 4" in the center of the dash. You don't have to replace these at all, the monsoon is actually pretty clear and I have added just a sub to many factory monsoon systems and they sound good.
I also dont reccomend changing them out if you are going to keep the stock radio on a non-amplified factory system because of the low wattage can actually damage aftermarket speakers after a while.