I have HM901, I have also ET MA9 and I used to have DX100 and DX50.
I must say that cowon was better than DX50. DX100 had superb fidelity and super effortless, I still miss DX100, I ordered its upgraded version (R10).
I wish DX90 is like DX100 but I have doubts, notice that DX90 has low voltage (4V), DX100 driven with opa627 at 8.7V is somehow different device.
I have HM901 that sounds superbly, but imaging was much better on DX100. opa1611 in DX90 sounds nice for sure, but opa627... well its different league.
I would be very interested to hear your impressions of the ET MA9, and how it compares to the other players. That looks like a very serious design, but I wonder if it's worth the cost (and its bulk) in comparison to something like the DX90?