Hi All,
I've played around with waterproof headphones and have found the H2O Audio stuff to be reasonable quality. The trick is getting them to stick and stay in your ears so water doesn't get in a screw up the sound.
I'm a drummer and have custom ear molds for my monitor headphones. These require a trip to an audiologist where they squirt goo into your ear and make a mold for silicone plugs that fit your ears perfectly. It's a pretty bizarre experience...
These custom ear molds, in tandem with the H2O Audio headphones are what Nat from Edge Kiteboarding uses almost daily. He swears by the setup (with a waterproofed iPod Shuffle). Here's what his setup looks like:
It's important to get the custom ear molds made for the specific headphones you're using.
I don't remember who made Nat's ear molds for the H2O Audio headphones, but this company seems to be aware of the right fit:
http://www.averysound.com/as.additionalearphone.html
It's a pricey endeavor, but I think the only real way to get good sound on the water.
Kirk out