If it's like mine, there will be two or three pairs of wires that the L&R speaker cables are connected to, that serve Zones 1 and 2/3. I only have two speakers, connected to the wires for Zone 1. The wires coming out of the unit for other two zones are just left as flying leads that are wrapped up and tucked out of harms way. If yours are wired correctly, you'll have the speakers for the cabin wired to the Zone 1 wires, and the deck speakers will be wired to Zone 2. You should be able to select which zone to play on your Simrad when it's connected to the same network as your Fusion unit.