another headfier chiming in:
Been using mine all weekend... the best thing about these phones is the portability. I was using them for mixing, connected them to my iPod and went to the office where I plugged them into my laptop. Never left my head
They sound excellent unamped, and very good from a 1G nano.
Isolation is very good and the seal ensures a consistent bass with any head movement. Comfort, a little uncomfortable, just enough that you move them around once and while to give your ears some relief.
Last year was very happy to have the HD-280s, before that the AKG K271S, and before that the MDR7506. All great headphones...though none perfect.
My initial impressions of the HD25 is they are like having better HD-280s. There is a sonic similarity. Wish I had them still for comparison. What I do remember, was that I was more than happy to let my HD280s go and keep the HD555s. The HD25 is in a different league. It bests both of these phones in sonic quality. The HD25 has a decent soundstage too, not as big as the the HD555, but not much smaller.
Recently I have been listening to my HD-555s less. I think I may be bored with their sound signature. In comparison, the HD-25-IIs have deeper bass and impact that is more controlled, with the overall sound signature being nmore neutral. This headphone is well suited to its application, perfect for engineering and monitoring. For percussion, the HD25 is more focused as well. The HD555s are great for their typical price though. I've A/B'd them, and both are great, with the HD555 being tailored towards its application of entertainment.
The good news for headfiers who may just want the HD25 just for listening - they are not as harsh as the MDRV7506, not as bass shy as the AKG K271, and are more compact than the cybermen sized HD-280s.
I got a fantastic deal, $100 CDN - lightly used. At this price these are easily the best phones I've bought. I'll still stand by the AKG K271 though, even though they're long gone. Fine phones.
Note: DJs may still prefer a coiled or longer cord as the one that comes standard with the HD-25 is quite short.