There are several possibilities here beertech. What sort of sonar are you wanting and how large of a display?
Whatever you get you will need the AS-ETH-5PXG 5-Port Ethernet Switch and connection cables for this.
Some models to think about:
859ci HD
859ci HD DI
899ci HD Si
959ci HD
959ci HD DI
999ci HD Si
1159ci HD
1159ci HD DI
1199ci HD Si