Ethernet will allow your 2 front units to use 1 xducer ...

You will need the AS ETH 5XPG switch to connect all 3 units ...
https://humminbird.johnsonoutdoors.c...thernet-switch

And you will need the AS EC QDE to connect Ethernet to the head unit ...
https://humminbird.johnsonoutdoors.c...-adapter-cable

Rickie