OK, that was interesting, but don't know what it means. Today, wired the two Helix units together without the network hub, still the same problem, put the hub back in line and played musical ports always the same issue. Went into network settings on the bow unit and changed 2D source from bow unit (which is connected to the US2 transducer in my Ulterra) to the Dash unit (which is connected to the HD SI transducer on the transom), and reset the sonar settings to HD SI transducer on the bow unit, all the problems went away. Changed the 2D source back to bow unit and problems returned, tried every transducer setting under the sonar menu and always had the problem with loss of SI and or Di sonar source. As soon as I changed back to dash unit for 2D sonar source, all problems went away again. Guess my bow unit just doesn't like being hooked up to the US2 transducer in the Ulterra.