Audio Systems: 2003 Passat w/monsoon upgrade, amplifier input, radio harness

Question
Hi. I want to upgrade my (2003 passat with monsoon) factory installed stereo with aftermarket Alpine HU. I know that my existing system comes with amp(3B0 035 456) and i want to leave it working. So I am not sure, how should I do wiring? How is that amp connected? Is it enough to do wiring in front?  

Answer
you need a antenna adapter with power and aaudio hig signal converter
the problem is that the output of the alpine hu is high 45w x 4
an the monsoon amplifier input signal is only 1 watt max

use this interface and it will let you keep the volkswagen amplifier, you also need the radio harness good luck

http://www.oemautosound.com/pc-598-176-oem-interface-differential-converters-uni...