The OEM HU has a connector for the optional pioneer underdeck or the bazooka cargo pod subwoofers. I am not sure if these are line level outputs, but it would seem logical that they were. You can buy the
harness from TRD Sparks. Crutchfiled also sells the Metra harnesses and PAC adaptor to make your own lineout setup. Spend the little extra money for the plug harness either way that you go. It is a far smarter alternative than hacking wires. My personal motto, "Don't cut what you can unplug". You can either "Plug and Play" or "Cut and Pray"; your choice.