Ok, first impressions of the Oyaide cable after approx 30 mins of listening. Please note, these notes are more objective than comparative, as my old cable was a bastardised stock cable which I'd cut, joined, added new connectors etc, and was worn out, so I can't directly compare it to stock, but will go off what I remember. Headphones are approximately 5-6 years old too, so have well and truly burned in. Also, I'm terrible at describing what I hear, I'm no good at the audiophile language.
I listened to a variety of stuff from Deadmau5, to Johnny Cash, to Billy Joel, to Bloc Party, Dave Brubeck, and other stuff. Most was 320kb/s MP3 or FLAC, played through a Samsung Galaxy Note II.
Overall, the HD25 and HPC-HD25 combo does everything right. Still has the deep, tight punchy bass. High end seems to be more 'tamed' than what I remember from the stock cable, no sibilance or harsh treble. On the Johnny Cash acoustic tracks, his voice is very crisp, and the pick can be heard on the guitar strings.
Deadmau5 sounded great, very strong and controlled bass, synths sounded awesome.
A worthy upgrade from the ruined cable I was using, possibly a worthy upgrade over the stock standard steel cable, especially for the lovely compact mini-jack. All the connectors appear to be of a very high quality, they don't look like they will break easily. Cable fits perfectly in the stock recess in the headband, length is perfect, and the connectors in the cups fit very snug and positively.
My only slight criticism is the cable does not quite have the same 'rubbery' feel of the stock one, it's very slightly stiff and seems like it could get twisted. It kind of feels like figure 8 cable. It'll probably soften up a bit over time though, so it's not a worry for me. Definitely not something to stop me buying it though.
Colours are awesome, gives a nice bit of life to a dull looking pair of cans, if that is of any concern to anyone