Just upgrade from the beta firmware to v0.97. Don't really sure what is the improvement as I have no had enough time with it yet.
Anyway, got a chance to do some quick demo of AK100 and DX100 yesterday. My impression so far is: DX100 is indeed a great sounding DAP. Though I haven't had HM901 with me, I can tell they are of the same level, more or less. Some said the stock amp card can be a bit underwhelming when compared to DX100, and I have to agree. With balanced card however, I think I would have prefer HM901 over DX100. AK100 is more of the same level as X3. If I were only to judge them by clarity, I'll prefer AK100. But it just lacks power. I max out on the volume (75/75) and I don't even think it is enough to be call deafening. At most, it is just louder than normal. X3 could easily match it for half the volume. The driver power also isn't great either, bass hit is noticeably soft. Also, I find the touch screen GUI to be clumsy. iriver could learn something from Apple here. I think I'll call AK100 slightly ahead of X3 on the cleanness alone (but not on functionality as a whole). It might be able to compete with DX100 or HM901 when used with a really good amp, but it is not on the same level if it is by its own.