Want to install a sub woofer
 

I want to put a 8in or 10in sub in the hatch were the crappy Bose sub is but I want to use the entire audio system (except the Bose sub)how can I connect a external amp to the factory head unit.

Use a mtx re q to add a amp just wire it to the subs inputs and hook up your new amp and sub.

http://www.the370z.com/audio-video/2...z-install.html

Here you go. 2 10's

I have an MTX RE Q you can have cheap. If that's the way you decide to go.