I received a factory Sirius unit for my 2005 Cabrio with the H/K radio. I received the factory install directions from MINI and was told that they were the same for the MC and the MC Cabrio. THEY ARE NOT! There is nowhere to mount the unit behind the panels in the trunk as recommended in the directions. The pillars from the rollbar are in the way. I did purchase the extension cable as recommended and the install bracket. I did not need the extension cable but the bracket made things easier. I also used the Terk Mini antenna SIR-MINI with Terk Sirius Satellite Radio Splitter and Adapter SIR-SP.

First you need to find the wire harness behind the right trunk panel. There is no access panel. Remove the black bolt and lift the bottom of the panel to get the harness. Once the unit was plugged in the radio did recognize the siruis unit. I mounted the unit in the trunk on a carpeted board attached to the rollbar pillar. It is visible but does not take up much room in the trunk and looks good ( I plan on painting the unit black to make it less visible). For the antenna, I ran the wire to the front of the car and mounted it next to the factory antenna(It is small enough that it does not look bad). I wish Mini would make a Cabrio antenna but this works. When they do I will replace the Terk. The whole process took about 2 hours (minus the hour on the phone with different Mini dealers telling me the the install is the same for the MC Cabrio and MC ).
Here are some pics.

https://www.northamericanmotoring.co...SCN0450_2_.JPG

https://www.northamericanmotoring.co...SCN0446_2_.JPG