That is a problem with just about any headphones out there once they get filled up with water when using the CTX. You must have the volume turned up to max and even then, especially if your hearing isn't the best, you will have problems.
I have been testing OBN's Skullie headphones for underwater use and they have exceeded my expectations. I have the Koss yellows, have had the GG underwaters and went through two pair of Amphibians and none of them came close to what OBN makes for volume on the CTX. I had to turn down the volume to 15 with the skullies, all other headphones had to be maxed out and then underwater I had trouble hearing. IF you scuba, there are the bone phones that are another alternative.
Somewhere on here or one of the other forums, OBN has a chart posted with the Decibel levels of the other headphones and the skullies.....I believe the bone phones are also included in that chart.... Just wish I could remember where it was posted.....it was within the past week or so.
I'm sure others will chime in here to offer their advice.
Good luck
Cliff