I received a heaven IV.
After running on FIIO new X3 for a while (till today), I found it's not a earphone best at sound quality.
I'm comparing it to a Grado GR10 (Yeah it's unfair but that's the only single unit left around me) and HD800 (for song reference), and the difference is very obvious.
Basically, it's GR10 with a low pass filter cut too early and too fast, and a compression with bass (I would describe it as a compressor at ratio of 2~3 running under a LPF of a few hundreds of Hertz slow rolling down, if this makes it more clear).
Details aren't outstanding, and I have to actually seek for those.
Vocal is a sad story. I would expect it to be better that this, but when a vocal flooded by bass and missing high harmonies, it's just.. well singer with a breathing mask.
Piano sounds like the lid is off, and a wooden container covers the whole piano in addition.
In summary it's that type like look nice, but sound cheap.
Will I keep it? Well probably yes. When outdoors, public transport, queuing, and so on that I want to separate the environment noise. In those cases sound quality is not the top requirement, and I can even bear microphonics of it when I'm not looking for sound quality.
BTW it sounds fine with trance. I don't have a lot of those, too bad.