Heya,
Just ran those tracks (albeit they are awful quality), and some others that are of high quality of some J-pop through a few of my headphones for kicks. I don't listen to this stuff often, if ever, so had to do a quick audition to get an idea of which headphone does what with it.
AKG Q701 - Quite nice actually, I find vocals always sound nice in a wider sound stage, no sibilance, nothing over powers the vocals, they're clearly the focus, no overwhelming bass, and the treble isn't spiked to the point of fatigue. Though I felt it was too analytical, a little cold, and reminded me that I was listening through headphones.
Hifiman HE-300 - Mids are actually kind of weird, there's a weird edge to it, hard to describe. The rest sounds great, good presentation, good sound stage. But vocals have an edge to them that sounds like a weird treble blanket or something, or maybe just a weird spike in upper mids. Not something I'd suggest for this genre.
AudioTechnica A900X (and the similar A900) - Right away, the vocals were warmer and more organic sounding. AudioTechnica I think was made for J-pop. The voices are flawless. The sound stage is great. Nothing over powers the vocals. The instrumentation is simply delicious. Hands down, this is the one that really grabbed this material and presented it in a way that made me lose myself in the music.
Shure SRH940 - Excellent vocals, wonderful presentation and sound stage for it. A little bright (this stuff seems to have very high pitched female vocals pretty much always), not much, if any sibilance. Instrumentation is nice, but the low end is definitely lacking for my tastes, though it's more suited for the ballads, less so for the j-pop stuff with some beat to it. Not something I'd use for this stuff as an entire genre. Again, great for the vocal/ballad stuff, but not so much for the tracks with a beat or anything with some bass in it.
Ultrasone HFI 2400 - Not up to the task, the vocals were a little distant and had a weird artificial feel to them, kind of cold. The bass is nice, but there's a lot of background noise and metallic weirdness to it, probably the spiked treble. The mids are obviously recessed here, so I wouldn't use them for anything that is really vocal based or focused. Great for electronic and some rock even, but not for things with vocals it seems. Sound stage was nice at least.
M-Audio Q40 - Nice for vocals actually, much to my surprise. The Q40 has some mids. They're a little muffled, not as clear as some others, and the treble is a little too smooth for my liking for this kind of stuff (I seem to like a little sparkle to give it a bit more emotion/edge). The bass is lovely, the beats are grooving. Voice sounds good, but again, not best here. Good sound stage. Everything is a little distant though, again, likely due to mids/treble compared to bass. Not something I'd get for this genre specifically.
Beyer DT770 - Great vocals, my first reaction was that everyone always says these have recessed mids, yet these sound fantastic for vocals, so recessed by popular theory or not, they are wonderful for vocals and I'm liking them much like how I liked them from the A900X. Sound stage is wonderful, good spacious sound, not too distant from the voice, but not right on top of it. Bass is not overwhelming at all, it's there and warm and gives it a body, some weight. The treble has a sparkle, something I really like with vocals, it gives it that edge, a touch of something to give it a little excitement, but is not sibilant and not fatiguing to me. DT770 is great for this genre. I'm quite impressed, as I didn't expect it to be.
Denon D2000/5000 - Vocals sound clear, clean and nice. A rich sound, organic even. The treble is a little more apparent here compared to some others, it definitely has more sparkle than the DT770 and A900X which both have been my favorite so far for this genre. There is a touch of sibilance, which I don't have in my other genres, so it seems that it's part of the tracks and less the fault of a headphone. Spacious sound stage, great presentation of all the instruments, the beats and the voice is still focused and up front. I'm liking this quite a bit, though I expected them to be great for this, as they are with everything for me. If you really like a bright beautiful j-pop voice, this one really pops, for lack of a better term.
Sennheiser HD650 (and HD580 by contrast) - Vocals sound good, but the treble is dim and sort of boring to me. Made me think of the Q40 earlier. Everything is clear and nice, a good body, warm, spacious sound stage, presented nicely. But for my preferences, not enough treble. I much prefer the HD600 (or HD580) in this sense for nearly everything, but especially here for this genre. Not enough bite for me.
Grado SR80i - Surprisingly great for vocals, the voice is clear, with a touch of grain, good body to it, warm enough to sound nice, but not too bright to the point of pain. Good overall balance for the genre. Not in love with the comfort, but the sound is right for it to me. I would prefer more sound stage, but it's still an option and quite a fun one.
Fostex T50RP - Vocals are ok, but it's weird, there's a dampness to it, not much sparkle, and it doesn't sound right. The mids are good, but it's basically all I hear, so it adds more weight to a voice than there is, probably because the treble seems so distant, and the bass is just mid-bass, so it sounds like any other thin headphone to me. At times it seems to be ok for this genre, but then it gets complex and it just sounds congested and the voice doesn't seem to be the focus of what I'm listening to, and that sort of kills it for me. Not recommended.
Hifiman HE-500 - I just melted. The voices are so natural, so intimate, so beautiful. My god. But this is not a fair comparison at all. Let's just say, reach for the stars. Excellent.
I sort of stopped there, I have others to try of course, but really I think I nailed it for my preferences down to the
AudioTechnica A900X followed by the
Beyer DT770 in the mid-tier price range. I didn't expect that as much. But there it is.
The A900X is what I would suggest at $250.
Very best,