Twice, have had both the GrayGhosts and Minelab yellows for a CTX. While the GrayGhosts are maybe a tiny tiny bit louder, they are still hardly loud enough to hear lower tones while submerged, ...for me. The yellows have more tone variance or range, at least for me and are a lot more rugged for worry free use (more trustable for submerged use / diving) and I could tell difference between tones better.
The newest version of the GrayGhost Amphibians (with the newest sound chambers, clear chambers with screws all around) would maybe be the answer? Called DetectorPro, but they said they don't plan to make these for the CTX, claiming that they "wouldn't work with CTX", so just gonna have the GrayGhost waterproof version.
KellyCo minelab repair said they could put the CTX connector on a set of the Amphibians, curious if the volume would be better...
Have put Amphibians on a few excals and they did great for shallow water stuff, kept yellows on my diving only one.