Upgrading from an SL40 to a SL30. I have searched the archives and this seems to be beaten to death, but one more time! I read in the Skyview installation manual that only a TX and RX wire connect the Skyview and the SL30, just like the SL40 does. It seems to me that there should be these wires for the Com AND a separate pair for the NAV. Can it really do all that stuff on one little bitty pair of wires?