Just tried the Io with the Iphone dongle, wrote down some of my impressions:
Vocals sounded weak and oddly pitchy, as though as it was over boosted, especially on female vocals.
Some bass, but it was of BA timbre, and didn't had much texture and rumble
Treble felt a bit rolled off, extension was poor
Overall I felt there was something lacking, the tuning does not sound natural on the ballads/pop songs that I auditioned.
However, the flaws became less apparent when I played electronic songs, so this genre could perhaps have been the intended one for the Io.
Another thing to note could be if there's any impedance skew, as much of the impressions here seem to vary from mine....
Would not recommend blind buying at all.