bozata

I have a 2005.5 2.0T A4 and want to install Phatbox. Unfortunately it is not pre-wired for a changer but for some reason it is prewired for XM receiver. In the rear-left side of the trunk I have the square female plug and 2 coax plugs (that was why I assumed it was pre-wired for XM). Pulling a CD changer cable would be ugly so I was wondering if I can use the XM plug to connect to the Phatbox. Does anyone know what adapter I need?

Thanks!