Bit of a late one here, I have a 56 plate Stilo with the bluetooth system installed (the limited Stilo Blu model)
I ordered an XcarLink USB/SD card version for my car thinking It would be a straight forward "plug n play", but having taken the head unit out, I found a mysterious black plug occupying the slot where the XcarLink was meant to plug in. Now, not knowing what this plug was (was guessing it would be the bluetooth system plug) I grabbed my phone, switched bluetooth on, then turned on the ignition (having unplugged this plug) and waiting for the phone to pair with the car......... Nothing. So, for process of elimination, I plugged it back in again and repeated the process, this time the phone connects, bingo, its the plug that controls the hands free.
So having contacted XcarLink looking for a solution to me not being able to connect both items at once, I start digging around on my broken upper glovebox lid, hoping to find a way to fix it, and after removing the glovebox liner, a little mysterious plug was found to be lurking next to the airbag unit, and lo and behold, It's the mini ISO connector for the CD changer, assuming it wouldn't be there normally as there's a plug occupying It's space on the head unit.
Here's the images I sent to XcarLink for future reference for them (and hopefully some use to you guys here)
Black plug that fits into the port the XcarLink plug shown fitted into.
And the mini ISO plug hidden up by the Airbag (with glovebox fitted!)