I don't know about iPod video or Studio V, but DX90 doesn't fall into my understanding of 'totally neutral' (though it is also very close) simply because of the use of electrolytic output capacitor, which can be avoided totally with a competent design (which I know iBasso is capable of) and I assume it is there really just for sound tuning rather than DC decoupling.
To your question however - I don't read enough on DX90 but I do get the same general impression of blandness complaints on many of the iDevices. As for Studio V - most Chinese do not like HiSound (the company) and bash it enough that it is almost impossible to tell a biased opinion from an unbiased opinion. Not for me anyway.
All I can say is that there are two different world ( market ) in this global. China and outside China, and how can people have different opinion about one thing . .
BTW, we will release some new models in the coming months, includes
E11K, X1, E10K, E12 (For IEM ).
Also, X3K is under developing . of course, it will not be released in the coming soon cause we are too busy.