I did not really like the H6 when it was released, a bit thin on an iPhone and a big headphone. And expensive. So I bought the B&W P5 instead. Quite good comfort and good sound. But.. I just had to give the H6 a try so I bought a pair a few days ago (the black model - after a lot of pondering).
I now have a completely different feeling about the H6. They sound very natural and good. I like how detailed and precise the sound is. You can hear so many details very well and how acoustic noises changes in frequencies in a wonderful way. They are also very comfortable, I don't get any pain on or around my ears but I do feel some pressure from the cushions on the top of the headphone after a while so I move them to another place on my head after a few hours. It is ok.
The biggest concern I have with the headphones is that they are so demanding. I have listened to them a lot on both iPhone and my MacBook Pro Retina and the difference is night and day. The Mac can drive them quite well on its own. The iPhone (5S) can drive them fairly ok but it is very obvious that the power output is much weaker. The sound is much more dull and you can't play very loud. I play music on my Mac at home mostly, not much noise to care about around me there. But I play music thru my iPhone on busses, trains and other crowded places - in these places the H6 doesn't sound very good on the iPhones output, it needs more power.
I am thinking about buying a headphone amp but I don't want to loose the headset feature (microphone, volume and answer buttons). I might end up designing my own Cmoybb-amp if I can design it to be very thin and send the data for the controller on the H6-cable. (I know I can use any other stereo cable but I want to be able to talk and adjust volume easily).
I still have my P5´s and I'll probably use both pairs since the H6 is much bigger but I am not sure. Will have to try them more before I know if I will sell the P5s or keep them.