I'm not sure what the exact specks are. I can tell you that they are not very high. You could swap out the factory sub with almost any aftermarket sub and it will take the power the factory amp has. I would probably go with a kicker. The factory amplifier does not produce super clean power though. Any sub is not going to sound as good as it would if it was powered by an aftermarket amplifier. Don't get a sub that can handle a ton of watts because these subs take a lot to make them sound good and your factory stuff will not produce enough power for it.
If you are interested, I have 2 8" JL W (0 or 1 i can't remember off the top of my head) subs. They are 4 ohm single voice coil. They take 100w rms and 300w peak each. They sound good and I believe they will fit in the stock box. I cam send pictures if you want. Asking $80 o.b.o. for the pair. PM me if interested.