The factory sound system came with a preamp for the sub. Should have been clearly visible when you removed the console if it were there. If you have the entire center console out and you see nothing, it may be tucked under the dash. If you are looking to add an aftermarket amp and sub, I recommend the Rockford Fosgate Punch series. Measuring approx 1x4x6, and requiring low airflow, you can put it anywhere! My rf monoblock is mounted to my driver's side and is nearly undetectable. I'll get a pic for you. Many shallow mount subs will fit okay, but a modification to the console to remove the extra storage will allow a larger shallow mount sub.
