Hi I purchased a 2004 Mercedes E320 it has the navigation head unit but I was told I need to purchase the DVD drive unit that goes in the trunk. I found the wires in the trunk that plug into it and wondering if anybody could tell me all I will need to make this system work. I also would like to use the hands-free phone option but don't know what I need in order to make that operate. Could anybody help me I would highly appreciate it. Thanks