You theoretically could, but it would not really be worth all the money you'd spend afterward, especially just for a 7 or 10 band passive eq. You'd have to tap into the signal wiring that goes from the head to the stock amp, and buy the passice eq. Then:
1. also spend at least 25 bucks for a signal to RCA converter, to connect to the new Eq with RCA inputs.
2. MAYBE you could just splice the wire and put an RCA tip at the end. That's JUST a thought. I'm not saying it will work, or won't damage the system. I don't know how much voltage is sent from the head unit as far as the line out signal goes for stock systems.
Then RCA outs spliced (or buying a another converter/adapter) to continue for the RCA to the amp.
After that, you've probably spent at least $150 for the eq and other stuff, plus labor unless you want to do it yourself. After that, it might be better just to get a new head unit with a built in digital eq. Ask your car audio INSTALLER for details, maybe he has better ideas. Ask the installer, not the showroom seller, unless he's an installer too.
