I've just returned from reacquainting myself with the z1r and comparing it to the th900mk2. I listened and compared some other cans while I was there, but i'll post my brief impressions of those in their respective threads.
the z1r sounded much as I remembered it, as did the comparison with the th900mk2. I've provided comparative impressions of both here before so all i'll add is that i really like the z1r. it offers what i'm looking for in a closed can - a warmish, relaxed presentation that doesn't mask the details. if the 10khz peak is there then it's not bothersome to me. it is the most comfortable closed can that I've worn and that's important to me in a headphone.
the th900 is brighter, more lively, has greater clarity and more "air" to my ears. I've always found it to be a very engaging can, dynamic and visceral. the midrange is more recessed than the z1r as I hear it, however. I prefer the th900's bass presentation.
the th900 is a closed can that sounds very much like an open one and the z1r sounds like, well, a closed can. they have very different sound signatures and I could happily own both but I won't be, so I have a decision to make.