2003 Saab with Alpine head power... no sound?

2003 9-3 saab convertible with alpine head and speaker amps (polk). I bought this car with this aftermarket gear in it. Just trying to get sound out of the head unit. I bought th metra 70-1784 harness and hooked it up properly. Head has power but no sound. I now found speaker amps under the front seat. Would like to get this unit as close to factory with aftermarket apline head. Should i disconnect the aftermarket amps? WHat to do with "blue wires on alpine head?