Well I broke down and got a pair of RS2i's I have to say I have been missing out, my old headphones (Sony mdr-7506) do not even come close to comparing.
How long do you think these should be burned in before there is no longer and change in the sound? Will it lose some of the high end harshness or add some bass? (my um3x's added bass after about 72 hrs or so and lost some of the sibilance in the upper end)
On some tracks I definitely hear the harshness that people describe coming from the high end. I find them comfortable as opposed to some other posters (which made me nervous about the purchase) uncomfortable headphones no matter how good just won't get worn.
I've only been listening to them for a little under an hour and honestly I think these headphones were made for Portishead. right out of the box it sounds awesome. My older music (Charlie Parker, Sonny Rollins, older jazz) unfortunately does not sound as good. But that's a source issue, not a headphone one. 30's 40's 50's even 60's and 70's recordings are not that great.
rock thru these is amazing, Steely Dan, Jimi Hendrix just awesome. Rush studio sounds very good, but Rush Live is missing bass. Primus doesn't have that sub thump, but you can hear that he's picking on that bass
overall a very fun pair of headphones, really lets you enjoy your music.