Yes they can Chris but the 787c2i unit would have to be on the whole time. Also any waypoints that are set in the 798 unit in the Si or 2D sonar will be off since the GPS Receiver (in the 787c2i) and the 798’s transducer are separated by XX feet. Good news is that you should be able to add a new GR50 GPS Receiver to your 798 at a later date by just plugging it into the Y-cable that came with the 798.