I have a 2004 a4 avant that came with Sirius radio,the guy I bought the car from installed a eclipse avn726e nav head unit in,I bought a Sirius tuner that's compatible with the new head unit,question is can I tap in the the existing antenna and power ect. That was used for the stock tuner in the back of the,and if so what adapters if any will I need if any,want to get what I need before I start to take the interior apart,any help would be appreciated thanks