I just bought a Humminbird 798ci SI HD Combo that came with a Transducer--XNT 9 SI 180 T. What I am wondering is should I go ahead and get the next step up HD transducer before I install it? And if I do does Humminbird have a trade-in (plus some money) for this transducer that I have? That way if I upgrade my unit I will already have the transducer installed. Thanks for the help.