2008 CX-7 Subwoofer Install Question

I have a Mazda CX-7 2008 I wanna install my subwoofer I have got told I need new stereo for it to work then got someone that says no I don’t so I need real answer how do I hook it up using one of those little square piggyback adapters? Can it work or no need answers ASAP as I don’t really wanna pay 200$ to get it installed