I am doing the same thing. I have bought a 5' cable to route my Helix 9G2N to the Ethernet box, its a AS EC SE 5 #720073-6 I do believe. Then I have two AS EC QDE 700 #720074-1. Plus the 5 port box #408450-1. I will be also connecting a Ulterra. The Ulterra came with a very long cable that I am using to connect the console 899 HD to the Ethernet box. I also plan on getting a Helix 7 with no transducer for the T/M as it came with a DI transducer built in. It will be networked into the system. I hope this helps you out, as I am learning about all of this. With the weather I have had my T/M on the boat for two weeks but not able to get out to get it all set up. You will find very good manuals on the HB web site.