I would go a little further than Mahstah
Don't use the automatic management of the GPS ports - disable it completely and get your GPS working with your AXIM 'directly'.
Once you have acheived this - then you can experiment with the automatic management, although personally I don't use it even though I have a choice of 3 GPS units (2*BT and one serial) and 3-4 GPS capable apps.
You will need to pair the units and assign a new incoming serial port to the unit. This will probably be COM7: (it is on my X51v). Check your GARMIN manual for the passkey to allow the connection.
You should then be able to establish a BT connection and use your app.