I own both hydra-x & hydra-x+. Yes, they sounded different.
I would say the former has better tonality on vocal while the latter has more transparency, power and punchier bass.
If anyone have read the review on 6moon probablly knew that they have replaced it with different brand of battery.
To me, it make sense that different brand or capacity battery change the sound.
How are you finding the perceiving sound stage size between the two? For example, Width, Depth, holography ...