I am going to take a shot and if I'm wrong I'm sure someone correct me. Put the 999 on console and use existing transducer. The 999 comes with the compact transducer if I'm not mistaken. Put that on troller and move 898 to front of boat and use that. You would have 2d, down and side up front. Don't see any reason for switch. Biggest draw back to side on troller is for good pics you have to hold troller pretty steady or your readings get kind of grainy and not to clear. Fish with a friend who has 998 on troller and it works pretty good. I usually run the troller when I fish with him and run finder. DI and 2d are both good.