I have a plug and play sirius radio (sportster 4) and I had been using the sirius supplied antenna. I was just letting the antenna basically sit on the dash, which was fine as long as I wasn't hanging any sharp turns or doing any autocrossing. I wanted a cleaner installation and hated that the factory antenna wasn't getting it's full use. I read at one time that the factory antenna could be used with aftermarket sirius tuners, but I wasn't sure how that would work with a plug and play because the tuner sat in the front of the vehicle while the stock antenna connection is in the trunk. I opened the compartment in the trunk and found the antenna connection and connected it to my plug and play unit and it does work! The problem was how to get that to the front of my car. I searched for fittings and extensions and came across this product. http://www.myradiostore.com/i/Render...re&s=inset
I connected it today at work and it is working great. I found another one on sirius' website, but it was 50' long and included a signal amplifier. It was designed for extending a home antenna. Just thought I'd let you guys know that this is available if you are trying to use a plug and play unit.

 

Looks good! When I was searching for an antenna extension for my install, all I came across were the long, amplified ones like you mentioned. I ended up locating my tuner in the pocket for the stock tuner and used a long Ai-Net cable to connect to my Alpine head unit. Not much help for a plug-and-play, but I figured I'd chime in that the stock sat antenna works fine for me too. Actually, I seem to be getting better reception with it than I did with the magnet antenna that was supplied with the tuner. I can actually receive a clear signal sitting in my garage with the door closed! Sound quality seems improved as well.