Dension Ice Link connection to RCD 300

I am going to install my Dension Ice Link Ipod lead to the RCD 300 unit in my Passat B6.

The lead was previously installed in my Golf Mk 4 with Gamma Radio Unit by a professional installer. When I removed the lead at the weekend I noticed that the installer had cut a bit of the plastic sheathing from a cable (brown) and wrapped the earth line from the Dension Ice Link around it with electrical tape.

Is the RCD 300 unit earthed and if so can I connect the earth line directly to the metal casing or do I need to do the same as the previous installation? If so, does anyone know what cable I should connect the earth line to?

I haven't looked at the back of the RCD 300 yet but assume the main plastic connector fits easily to the rear of the unit as it did in the Golf.