I honestly wouldn't waste any time or money on the cabin speakers, unless you want it loud in there. If you use the Sinister amps, I recommend 1 808 per channel. You can pair 2 650's per channel on that amp too. If you really want the cabin speakers, you could set up front to rear fade, that way you can turn down the cabin.

In a perfect world I think I should probably run the cabin speakers off the head unit then the four 808s on whatever matches well.

If you do that, you'll need something more efficient. 650's won't work too well on a head unit. Impedance is about 3.7 ohm

Maybe I'll leave the Sony stuff in the cabin since it is already crazy loud in there.

Tell me about using using the Sinister vs SYN DX for my application. Is it just that the Sinister has a little extra power over the 808 rating?

99% of the boats I've done have all left the cabin speakers alone, unless they were trashed.

Yes, the Sinister is a better platform. Both are great amps, the Sinister amps just have bigger balls. Both are class D, so they're the most efficient and won't have thermal issues.

I have a set in the boat & a set on the transom. I also have a set of 650's in the arch, all ran with SD amps... Sounds good to me. I'm not real impressed with the 10's but they are a free air sub so they will never pound like a good sub in a custom built sealed or ported box...

I can agree with that when you don't use an enclosure, but that goes for just about any infinite baffle speaker. The XS10FA's do okay with around 1 to 1.2 cu ft.

Looks like for the money, I might as well buy the six channel and find a place for another pair of 808s. Haven't heard them before but I'm guessing at 150 RMS a speaker...x6 it will be plenty loud.