Rockville RXM8BTW Marine Amplifier Setup

Need some advice on best way to configure this

Here are the specs
Rockville RXM8BTW 8 Channel 1500 Watt Marine Amplifier W/Bluetooth White
1500 Watts Peak System Power        750 Watts RMS System Power
RMS Power Output at 4 Ohms: 65 Watts x 8 Channels CEA Rated
RMS Power Output at 2 Ohms: 95 Watts x 8 Channels
RMS Bridged Power Output at 4 Ohms: 190 Watts x 4 Channels
Peak Bridged Power Output at 4 Ohms: 380 Watts x 4 Channels.
Configurable to 8-6-4 channels or 6.1 or 4.2 System

Boat has
Six. 8 inch 100W RMS / 300W Peak speakers
one 10 Inch 150W/300W Peak SubWoofer

The head unit is only a 4 channel head unit. The original amp (which still works) is only a 2 channel
Does it pay to use it just for the Sub? Or will it be too strong?
400 W MAX Power @ 2 Ohm x 2 Channels
200 W MAX Power @ 4 Ohm x 2 Channels
800 W MAX Bridged Power @ 4 Ohm x 1 Channels
RCA Low Level Inputs, High Level Inputs, Fixed High Pass Crossover, Variable Low Pass Crossover

What are my best options? Many thanks


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REX