My experience was similar to yours in comparing the two headphones. In fact, I couldn't understand why anyone would want the X when the XC seemed to sound "better" IMHO. However, at my senior age I do have a bit of a high frequency hearing loss. Nothing severe but perhaps enough to account for why I prefer the XC over the X by a lot. I guess input from those who have normal hearing would be of interest.
11/6/16 at 7:05pm