Question for the audio members here.

Any professional installers in here? I plan on taking out my stock sub woofer in my 9speaker stock xls system. I want to just upgrade the stock 10" sub. I know I am going to have to add an amp already. I also know I have to use a Line level converter. Heres my question, how the heck do you wire up a Line level converter to the amp? Also is it possible to use the wiring that comes from the stock amp going to the stock sub in the converter and still have controll of the new sub from the head unit?
 
Any drawings describing the wire would be awesome. Maybe some color cordinated wires haha.

hit me up on aim, later, and i'll chat with u bout it bro. I forgot about u the other day, my bad

Ill be on later.