Can I just upgrade my stock amp, put an aftermarket one, do the wiring to the OEM sub (8in) and to my new sub(12in) and it still hit strong?

 

Sure. If you have the money and know-how, you can do just about anything. If you're putting a 12" sub in the trunk, why bother with the 8" oem sub? I can't imagine it will sound very good having both going at the same time, the oem sub is 2ohm also, whereas any aftermarket subs you'd get would be 4ohm or above probably.


I would just add an amp to power the trunk sub and don't worry about the oem 8". It is only rated for I think 40w anyway. If the stock amp is still working, let it continue to power the stock speakers. Turn the subwoofer control for the oem sub down on your head unit and then have a separate gain control for your trunk sub and all will be good with the world!