Looking to add a amp and sub.

[Nikon]

I have a 2010 Jeep Grand Cherokee
It has the radio with the screen and navigation and the XM
What would I need to hook a sub to the back of it, is there a extra port input etc?
I once had to buy a extra box to add anything to factory radio on a car i had

thanks in advance

 

[Tison78_CJ5]

My '96 had a power amp. under the rear seat, for the rear speakers, that was factory.
If yours has the same, it should be pretty easy.
With all the changes, adding the computer to the stereo, and all. It has gotten harder to do, without a factory mod. from the dealer.
good luck.