The CDX6 radio COULD be used in other applications, though I would NOT recommend it for a marine application. First would be a concern regarding humidity and water. This radio was not intended for marine applications, so has no water-proofing covers, or seals on the buttons.
The second reason is that the mechanism in this radio is quite delicate. Radios are shipped to the factory with a "shipping bracket" installed to protect the mechanism. If you buy a used radio, you will not know how it was handled - it's a good bet the mechanism could get damaged just by UPS shipping.
So, unless you're planning to pull YOUR CDX6 out of YOUR truck, and put it in a pontoon boat with an enclosed helm on a very calm lake - I wouldn't try it.
regards,
cobrajeff