Stock Navi vs. Garmin, TomTom etc...

The stock DVD navi that comes on the GTI vs. TomTom, Garmin, Magealan etc.. what's the difference? Do you have to have a DVD with maps loaded into the stock one? Can you listen to music while using the stock navi? Do you have to have any additional antennas sticking out of your car with the stand-alone units? can you integrate your sound system with a stand-alone navi? thanks for an responses...

-HTL

No additional antennas needed on stand alone units and the maps/software comes preloaded on the standalones. If you want to update the standalones you can do this by hooking them up to the computer. The factory units require a cd to update. Dont know much about the factory unit. I sell the others at work so those I know.