I would say for the HD-650 (ONLY!) it's comparable in sound to the Fiio E9.
I tried about 5-6 different sources with the Vali and HD-650 and can't hear them with the Vali.
However, the Vali is very good with my modded Q701.
I'm a little disappointed I don't like it much with the HD-650. O2 and even the Magni is far better for the HD-650 (IMO).
The soundstage of the Vali is very closed in and doesn't do the HD-650 any favors. Vali also has very farty/loose bass with the HD-650 and any source i've tried. Maybe you could buy a $10,000 DAC to fix the Vali's problems.
EDIT: The only thing for me that could save the Vali with the HD-650 is that if you had a DAC with a massive soundstage and it had about zero warmth.
Strangely enough the Vali with the Q701 sounds dead neutral.
Edited by tdockweiler - 12/3/13 at 11:58am