I have two Helix 10's and an Ulterra with I-link networked. They are not Mega, but have the latest software updates, and I have to have two cards. I usually run a Smartstrike card in the dash unit and a Lakemaster Plus card in the bow unit. I have tried only one card, it won't work unless I want to move the card from one unit to the other during the fishing day. I use the US2 transducer in the Ulterra for the bow depth and the SI HD transducer on the transom for SI and DI on the bow, then the SI HD for all three on the Dash unit. Love the follow the contour option the i-link gives me when pushing jigs and cranks.