The cable Mitch sells replaces the LCD button panel that comes with the HD tuner. This allows the unit to plug into your serial port and lets your computer control it. Sound is run from the stereo RCA jacks to the line in on your soundcard.

Regarding the antenna, the unit acts as a passthrough. It has an antenna in and antenna out to go to your stereo. Considering this runs off your car's stock antenna, it will probably get the best reception possible.