Sub and Amp Hookup on Stock Stereo?
 

Hey, so I got 2- 12" Alpine Type R's and a 2000w Alpine amp. Don't hate, I bought it from a friend. Anyways, can I set this system up in my 2009 Mazda 3 using the stock stereo, or do I need to buy an aftermarket head unit as well?

Any help would be much appreciated.

You don't need an aftermarket HU, but you will need a LOC (Line Output Converter) as the stock HU has no line out for an external amp. The LOC taps the speaker level output and converts that to plug into the amp's RCA inputs. Alternately some amps have a speaker level input on them and you can just run the speaker lines to those. The LOC is probably easier though.