Unless you are referring to the Gateway and backbone connections Your HDS unit will work with the built in Tducer.If the plug is different there are adapter cables to utilize the built in Tducer but the Tducer is 2D only. My Lowrance 5HDI fits the Xi5 plug.
As far as the Fpedal did you try syn. within the 10 second time frame? It took me a couple tries to get it right.
Bass Pro told me you dont want to add an external transducer to the i5 because the transducer cable will get damaged from the motor turning the way it does. I mounted my console and bow sonar tranducers on the transom. Not the best situation but I cant afford to upgrade my HDS unit allowing me to use the built in transducer on the i5. I love the t/m but I still havent been able to get the foot control to work