Audio Retard

Okay...I am in need of some help again. I have an 03 Mobius LSV with the Kenwood CD player, amp, & tower speakers. I got a new amp from my brother for my birthday and I was wanting hook it up. I know absolutely nothing about audio equipment, but I know where the amp is located and I wanted to install the sub box down next to the amp. What is the best way to hook it up to maximize power, while still allowing all my other speakers to still use the same amp? Is this even possible? I'm assuming it is since a sub is a factory option. Thanks in advance!