I'm calling it now: the KEF M500 is the single best closed portable headphone that I've ever heard to date!
These headphones are seriously awesome. They're also way better than the V-MODA M-100 and Beyerdynamic DT1350. These are the closed portable headphones that everyone should be buying! They look awesome and sound awesome! I officially give the M500 an A+! It's so good that I don't feel the need to continue the journey for a closed portable headphone! (Well, aside from the Audio-Technica ES700 which I've been curious about.)
The M500 earns my highest recommendation possible! Its sound shouldn't be possible at $300! I'm a fan of the MrSpeakers Mad Dog 3.2 too, and would prefer supporting an American business if I could, but even the Mad Dog sounds unnatural after the M500! The M500 has this all over the Mad Dog too. And it doesn't have the amping requirements of the Mad Dog either. It's rare to find a great-sounding headphone that's also refreshingly efficient!
I love these headphones. I could nitpick them to death if I really wanted to, but that would miss the point. They're the best small closed headphones that I've ever heard! Heck, there are CDs where I'd take these over the Fostex TH900 too! The only thing that would be better would be the Grado HP1000 itself, or the Stax OII MKI, or a sonic merge of those two.
Anyone who listens to music owes it to himself (or herself, as the case might be) to buy these. I love these. The M500 is my new favorite headphone!
After all the praise you have given the M500, I was quite surprised to see that you'd sold yours.. so I just have to ask, why'd you do it?