I just wanted to say that after measuring a 60hz sine wave played via cd i found that the head unit would output 5.98v at full volume.

So its safe to assume that it outputs at line level. I taped the factory wiring and ran it to a separate amp and it works great! no distortion.

If you wanted to add subs with the stock head unit all you have to to do is tap the wiring for the input and remote of the stock amp. Make sure your amp can handle 6v pre amp inputs.