02 Intrepid proper amp?

I just recently installed an aftermarket head unit into my 2002 Dodge Intrepid. The car has the premium sound system and I want to add a crossover unit and another amp for a sub. Can I splice into the wires from the stock amp for power and amp turn on signal, or would I have to run new power wires to the battery? This is my first time installing an amp and sub in a car so any help/tips will be greatly appreciated.

Sorry, I accidentaly hit enter before putting the proper subject for this post. Anyways like I said above I want to add a crossover, amp, and sub to my 02 intrepid, but have almost no idea where to start. I managed to install an aftermaket head unit by myself, but I'm not sure how to properly wire up the crossover and amp.

My ideal setup would be head unit -> crossover -> stock amp and aftermarket amp -> speakers and sub with the stock amp powering the stock speakers, and the aftermarket amp powering the sub. The crossover has a low pass and high pass output but they are both RCA only. Is there a way to adapt the stock amp to accept an RCA input, or would I have to buy another aftermarket one? My other idea was to leave the stock amp and speakers alone and just use the crossover's low pass into the aftermarket amp for the sub.

You can what you want to do but your better off getting a monoblock and running your sub separate

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Pioneer 8200 nex
Audiopipe 1500.1
Audiopipe apcl 2004
Alpine spr-68s
DD712

The best way to go is to completely bypass and remove that factory amp if you are wanting to run a crossover. Meaning you will need a 4 channel amp for the speakers and an amp for the sub woofer. Bypassing the factory amp will mean running new speaker wires for each speaker, but you will thank yourself later. It will save you the hassle of trying to integrate systems in with the factory amp. It will also sound a whole lot better in the end assuming you are using quality amps and crossover.