Audio installations in boats aren't usually well done as the designers of the boat never allow enough space for them. Space is always at a premium on board. A buddy of mine sold his Cabo 40 Sportsfisher this year (which he bought new more than 16 years ago for over a million dollars => Canadian $ - not real money!) and the best "stock" system he could get from Cabo was a Bose Lifestyle Home Theater (5.1) set-up with those little dual cube speaker arrays. For a boat, and I've been on lots of them over the years, it wasn't bad but no where near audiophile levels. (Not even good car audio levels.)
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@Eppie I'd suggest something like the those outdoor surface mount Polks but with a Sub integrated. Maybe a small in-wall sub? Close the Cubby door if you can to improve the Sub's performance in the main cabin. That's a very cool Boat!