Hi knightsquad,
I just finally got to try out my waterproof headphones, and they definitely do sound different, I've only tried them on land, sounds seem more muffled to me, it's hard to explain, one thing I did notice when going over bottle caps in my yard was that the "hi low hi" tone of a bottle cap was more easily discernible than through my normal headphones, I don't know why. I used them for a couple days to try to get used to them but the sounds definitely were different and for me, it seemed it would take some getting used the different tones all over again. The low grunt of iron is lower in the waterproof headphones and I think all sounds are basically lower in tone due to the quality of the speakers, and the "containment" of the sound (for lack of a better term) due to waterproofing. They will definitely take some getting used to for me, and I was afraid I might be missing something while using them. I'll have to see how they work in the water for me.
If I find I have trouble with them, I may try the Greyghost headphones, I don't want to give up quality of the sound to the point that I miss targets, I know I've seen people use them with apparently no issues in plenty of youtube video's, like Aquachigger for one, he finds tons of relics and coins with the blue headphones so I imagine it is just a matter of getting used to them and giving them the chance to learn them. They seemed to me that they would require a fair amount of effort on my part to get used to though.