I like the CK10. It's a good product at the $200 price point, but it does need to be EQed. There's a sizable peak at 12kHz that can be rather strong in some musical situations. J-pop could certainly be one of them. It tames out a lot with some EQing, however the response shape is a bit odd, more of a skewed triangle shape then parabolic and because of the response and level of detail it has on the top end, it's a bit sensitive to gettting it right. Without EQing, the CK10 can be a bit sibilant, lot of strong Ses lol.
I don't feel it's terrible, but like with most earphones, EQing can generally make them better. With some earphones, EQing can be a game changer, like my OK1 buds. The CK10 isn't amazing with soundstage either. Other earphones give a more spacious and layered experience.
Frankly, the UM3X is one of my favorite earphones and the only thing I've used that I kind of regret selling. There's only two earphones I've used that can really pull me into the music and provide a seriously emotional experience, my Ok1 buds and the UM3X I owned, but unlike the OK1s that benefits from a lot of EQing and a robust amp, the UM3X is well balanced out of the box and work off minimal power (although bass can be oddly muddy and incoherent off too little wattage). I keep trying to be a one earphone man, so the Ok1 stayed. I just keep buying new stuff though and weed through a pile of more products from time to time trying to find a sucessor. If I were to have two, the UM3X would be my other though.
Gameboy115, UM3X
less dynamic? I haven't used another earphone that's had as much dynamic breadth and energy of note as the UM3X.
By the way I've been listening through a bunch of random j-pop as I typed this just to be in the mood, lol.