For the ZLD its acts like a Fader, and when you turn the tower down it lowers the input voltage to the amp, so the amp is running less, not wide open with it muted per say.

When i went from the Factory Kickers to the Exile cabins it was a huge improvement man not just volume wise but sound in general. I have always liked the kicker speakers but to me there is too much tweet when they get loud and they just scream at you then. The SXM cabins have a warmer sound and surprising they can handle a lot of mid bass.

I would replace the cabin amp due to it most likely being a 250.4 kicker and thats not enough to run the Exiles. I would get the 800.4 to go with it. Then the cabin of your boat will rock so much you can just crank it up when surfing and just keep the towers at 50% so its not blasting way behind you.