My thoughts are that they are a bit different. I believe it has to do with the CTX being more accurate AND the CTX's more use of the FE 12. The older Explorers had more of a flute'ish shound when you hit a deep copper or silver. I believe the tones of the machines are generated by the numbers (FE/CO). I don't believe it uses a separate tone generator from a different source. As such it is the FE & CO numbers that determine the tones. The older explorers had the good solid CO, in most cases, but the FE has a tendency to fall all over the range. This bigger drifting of the FE causes the flute tone we love so much on the older models. The CTX works harder at taming that FE number and in doing so has less of a flute tone.
I love everything about the CTX far more than the E-Trac, for example, but I do like the tone of the E-Trac a tad better.