If your car was available with the same headunit without the external amp then I would assume the amp has speaker level inputs. However, if it doesn't, you would have to know the line level of your existing unit as well. The Clairion you mentioned has 4V pre amp outputs (no speaker level). The stock amp will need to be designed for 4V preamps or you will run into low max volume or the ability to cook your amp very easily.
BTW: my head units connects via fiber to CD changer only. The amplifier connections are copper.
BTW: my head units connects via fiber to CD changer only. The amplifier connections are copper.
