A little confused here...
You say your speed is being displayed as 0Km/h, So you must have Advanced GPS enabled. This means you shouldn't be going to "GPS Settings" to set up the com port but using the "Destinator 3 Frontend - Configuration" shortcut under the "Advanced GPS" tab.
But then because you're using SiRF, advanced GPS (NMEA only) won't work! If you want SiRF, turn Advanced off
If you want advanced GPS, use NMEA and configure the com port in FE config and not destinator!