Mercedes Becker Radio

my car currently has factor head unit (radio/cassete player) and trunk unit (factory amp). I removed the factory radio and unplugged all its wires.

What I need to do know is hook up the aftermarket radio but I need to bypass the car amp so it instead uses the aftermarket radio's amp.

I called best buy they told me to bring it by but they said to bypass factory amp alone is $150. This was disappointing to hear. I know people can bypass the factory amps themselves with a simple kit. How can I do it for my specific car.

oh the factory car radio/amp is a becker model BE1432.

oh and another quick problem - my car's alarm will go off if it thinks the radio is stolen once the car is alarmed. Since I took out the radio, if I lock (alarm) the car and leave, 5 minutes later the alarm goes off - it thinks the radio is stolen. So I basically cant lock (alarm) my car.. its annoying!