Okay, just finished A/Bing the HP50 and M500, and I have to admit that I think MH is spot on with his ranking in sound quality. The only think the M500 clearly outshines the HP50 in is treble. But I could basically care less about treble in the grand scheme of things (as long as it's adding to the clarity and transparency of the headphone). And that outshining isn't by leaps and bounds. And acually think the HP50 has more bass than the M500, it's just the soundstage is much wider than the KEF, and the bass, mids, and treble are tuned to be more neutral. Yet the bass reaches down when it needs too. Now, the M500 still holds its own against the Viso, but it presents a more intimate or smaller club sound than the HP50. Again, I'm not a treble fan, but the treble in the M500 is pretty amazing without being harsh. Right now I would say there's a tie in my enjoyment between the HP50 and On1 (haven't A/Bed these two yet but I know), and the M500 lagging just somewhat behind. So is the HP50 a lot better M500? Not really. They have some similarities, but enough differences in the sound signatures to stand apart on their own. If I could only have one, however, I think I would have to agree with MH and go with the HP50. I still enjoyed the KEF, however, quite a bit when I had them on my ears.But yes, the HP50 is the better performer.