you can do either or. To hook in a hew HU would be a complete BIA, and youd still need your old hu in the car in the trunk or somewhere. if you want your subs its easy. by a low level adapter. rig it to the stock sub wires in your car. itll turn those wires into RCA's connect the rcas to a new amp and there you go. I did the same in my 97 ETC only difference is i connected the adapter to the two 6x9s on the rear deck. The coolest thing about this is when you adjust the bass on your hu. the bass will slam more out of the new subs w/o having to adjust the amp.