I am kinda in your boat also. I have the IPilot like yours and it works fine with a standard HB DF (565). As I understand it, you can use down imaging (down scan if Lowrance) with the US2 built in transducer but not side scan. I can see how moving the transducer around would screw up the signals on a side imaging unit.
I plan to get a DI/GPS combo (7") for my console and move the HB 365 combo from my console to the front. I may go with a DI/SI combo if I can afford one.
Am leaning toward the Lowrance based on the screen shots I've seen on here. Always had HBs but the resolution does not seem as good as the Lowrance.
Mark 1:17 ...I will make you fishers of men