I did compare them about a month ago but... anyways...
"Currently listening with the z1000 with Mundorf Cable and cd900st with Stock Cable in a more quiet room (my room) and I can definitely say now that the z1000 indeed has a lot better detail retrieval in the upper midrange and treble region. I can hear both micro-details without listening really hard to the songs but the z1000 produces those micro-details much more clearer. Not to the point that it sounds harsh. It still sounds smooth but the upper midrange to treble region is more prominent than the cd900st. On some instruments, I also find the Midrange are about the same but I still find the z1000's midrange sweeter but not as sweet as an LCD2 or sm3.
On the other hand, cd900st sounds smoother and laid-back on the frequency range that I mentioned above. With this, it feels like that cd900st has bigger headstage now and I don't know why that happened as I always know that the cd900st puts the whole mid-range region forward, but now it isn't anymore, specially in the upper mid-range region. Maybe because of the source? or burn-in? The cd900st has about 200-300 hours now while I am not sure with the z1000 but I'm guessing its around 100 hours or less.
Both headphones have accurate bass that doesn't sound distorted even with bassy tracks. Both headphone's bass are somewhat lacking for other people, but they are enough for me. Note that I'm not fond of bassy headphones.
Now for the obvious, the cd900st is still more comfortable but the z1000 gives a lot better isolation and better clamping but not to the point that it hurts your head with the clamping."
I'm using the DX100 as the source. Also, I did not adjust the volume so the CD900st sounds bigger or wider due to impedance difference. I could give it a second whirl sometime though.