Working on a couple boats for other teams this winter. One with ICON digital dual binnacle to control 3 motors, one with Livorsi. The old and the new so to speak.
The engines have servos to control the shift and throttle. Center motor is slaved to the left stick on the control. The ICON system syncs the engines and allows for rpm tune 1% up or down at a time. The center motor is kept in neutral if the port and starboard motors are in opposite settings for gear shift for maneuvering. There is one backbone cable which runs to the back of the boat to a network hub. The network hub then splits and each motor has a backbone cable from the network hub to control throttle/shift/start/stop. Nicest thing might be the new 5" gauges they have.
I should add that via laptop you do have to assign each engine to its place on the network (port, center, starboard) so the system knows what to do.