Andy-
I see from your profile you are from Joplin. I assume Joplin MO, and therefore fresh water?
I work for a stereo company, specifically selling audio equipment to boat manufacturers. I have purchased product from Rock the Boat as a part of competitive analysis, and I can tell you my experience with them has been good, with timely and careful shipping. IF you decide to go that route, I think you will find the experience acceptable.
For your needs, assuming you are not sailing in a brackish or salt environment and assuming your stereo is down in the cabin, I will recommend that you will be fine with a normal car audio CD player, as Tim suggests. Much of the "water-proof" stuff is designed more for those exposed open applications typical of a family runabout, or for sailors and boaters in coastal regions.
Precautions are still in order. For the power and speaker wiring, make sure that the wires enter the back of the radio from either a low angle or bend the wires so that a drip loop is established. This will keep an water from getting in the radio on the wiring. Consider a light plastic sheet, (like from a plastic report binder) over the top of the installed radio to protect the "innards" from any possible drip leaks, like from a stanchion or other thru-bolted hardware. These simple precautions will prevent a lot of potential issues.
Your speakers on the other hand need to be designed for the environment, at least any cockpit speakears do. Look for speakers with sealed cones to prevent water from getting into the speaker motor. Look for magnetic shielding, especially if you are mounting speakers on a boat where a compass is used. Look for speakers that meet or exceed standard tests such as ASTM B117 and ASTM G154; these two tests are for all materials and test for durability in UV exposure and for a salt-fog environment. Look for aluminum or injection-molded speaker frames; ideally, look for a speaker that has as little ferrous material as possible, including the mounting hardware. Exposed steel will rust eventually and rust leaves nasty permanent stains in gelcoat. Try to verify that the mounting hardware is 304 or 316 stainless and if you have any doubts, use mounting screws from your local chandlery to guarantee you are getting good stainless.
I am unsure about the specifics of you satellite radio question. What sat radio receiver are you considering using? Most satellite installations I have seen use an antennna, but your application might very well be different.
Sorry for the expanded thoughts on the speakers, but it might prove worthwhile to you, or to somebody else.
deck and 10 disk CD changer. The cassette deck has a cassette for plugging in the iPod. It also has a wireless remote. It's satellite ready. Plays everything except 78 rpms! Also added a powered subwoofer last year.
