Sailboats and Audio

Currently I am in the market for a 40 foot sailboat. The problem is the audio systems are just rehashed car systems. Does anyone out there have any suggestions. You cannot have in-wall on a boat usually without compromising the structural integrity, on-wall is very acceptable. Marine grade (that is water resistant) is probably not necessary because it will be in the cabin, and doubtful whether I will have any speakers in the cockpit. I thought about a 120 volt system but that would require a very large capacity inverter and/or generator system, which is ok.

Can you get the Mark Levinson car audio stuff separately without purchasing a Lexus??

Any suggestions would be greatly appreciated!