This all depends on your budget and audiophilenuttieness . . I like to tell folks to step back and take a look before they spend a penny. I have been through a number of installs and seen a number of folks (past life) spend a lot more money than they should have because they add to and change their system. A planned system never costs more money.
A great example, MANY peeps add an amp for their speakers and then decide they want a sub. In many cases they did not use the proper gauge power wire and now have to start over. Or worse yet they risk a fire by using underrated power wire.
If you KNOW you will be happy with a some speakers and a new head unit. You will be happy with just about any decent quality stuff. At the lower end of the spectrum you can't tune enough to make much of a difference with off the shelf products. I personally would look at marine or high UV rated speakers. Most marine apps have UV protection and help protect the speakers from the sun. BTW, if you look at most marine rated stuff - they cover up the drivers pretty well for this very reason. Most folks are worried about moisture . . .but the biggest issue is the "surround" being chewed up by sun exposure. In most freshwater applications moisture is not the “biggest” issue.
My prefs are Alpine for the power/signal and Polk & Image dynamics for the speakers and subs. Alpine has great ipod interface. Polk has some decent speakers for the lower end budget (they have higher end also). Image dynamics is on the higher end and more pricey, but their subs are amazing! True audiophiles would say my equipment choices are low to middle of the road, but in a boat you can only tune so much even with very nice equipment. At home I would use brands most folks have never even heard of.
Polk makes a good coax called the Polk MM650 - soon to be discontinued so you can find some great deals. These are high UV and carbon fiber cones.
Plan ahead then spend wisely.

MMC6500


Notice how the drivers are nearly impossible to see on the Infinity. This does affect your SQ as well.
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