It might just be a preference thing (regarding the th900). When I did the store demo I thought the 900 were very good, but at home and comparing against the HE6 there was no question which I preferred.
The HE6 with the MHA100 is the best I've yet to hear them. I should note though that I haven't used them with any of the über HE6 speaker amps favoured in the HE6 thread. Amps I've tried the HE6 with: Naim Headline, Mapletree Ear+ Super, Fostex HPA8, Audion Silvernight 300B, Naim Nait5i, Nuforce DDA100, Leben CS600.
At the demo I also tried the store's HD800. I've never really liked the HD800 when I've tried them before, with a couple of different amps. Yes, they were technically very good but didn't connect with me. But with the MHA100 it was the first time I felt they really might be worth buying.
thanks for your answers. Very helpfull.