So I just got a new boat (new to me) I am looking at buying new helix units. I am looking to set up the units exactly like I had my humminbird (1197si & 998c si) on my gambler. Here is the setup I need. I want individual SI transducer one on the back one on the trolling motor. (I don't want to share a si transducer in the back of the boat) I also need both units networked for way point sharing. I also want an external gps antenna. Can you order the units without an internal antennas? Lastly I'm debating between the helix 10 or 12. Are the helix 12 with Chirp worth the extra money? If I am misinformed please correct me I am going to order the new units this week!