edit: I switched to PC so I could type this for you.
The cable comes down from the roof on PS pillar, under cover. Here I dissembled the connector, and installed a 1' or so extension cable. This factory connector IS a coax type round connector but it also has a plastic square outer layer that snaps. It plugs in perfect to the Sirius size antenna connectors used in the last couple years, but I think I had to remove the factory plastic connector cover.
Than I dropped this extension down under the dash, along with the end of cable that came up from radio
I have a magnet antenna that I Hide under hood when not being used. when it is being used, I find it really needs to be in center of hood to work perfect. I routed the end of this magnet antenna connector into the RF fender well, than through a rubber grommet that come out under RS kick panel and isolated it with some plastic wire loom I have. Route this also to under the glove box areas.
now I have 3 cables under dash. one goes to radio, one goes to magnet antenna and one goes to factory antenna.
All I do is pull magnet antenna out from under hood, put it on center of hood, drop glove box, and switch the radio pig tail to plug into which ever antenna I need.
All I listen to is satellite radio so its kind of important to me that it works all the time.