Factory Wetsounds Power/Ground upgrade question

Just took delivery of this boat a few weeks ago and already looking to upgrade the 10" subwoofer to a 12"
Poking around and looking at the Moomba factory Wetsounds install and noticed they're running 8 gauge wire to the SYNDX4 and SYNDX6 and 4 gauge down to the battery switch. Looking at the manual and Wetsounds recommends 4 gauge. I'm assuming since the runs aren't that long then the 8 gauge will suffice? My question is I'm looking to upgrade the subwoofer amplifier to around 1000 watts and all amplifiers in this range recommend 4 gauge or higher.

I'd like to leverage the stock setup and install the subwoofer amplifier and tap into the terminal 4 on the distribution block. Would 8 gauge suffice for the subwoofer amplifier? I guess my question is do I need to upgrade to I/O from the distribution block? Or would the 4 gauge be good? I know I would need to upgrade the 150 amp inline fuse and circuit breaker.

Any feedback or suggestions would be appreciated!
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