Have Fiio explained why they choose their sound signature then, and what that is? Sorry if its something obvious, but I don't have much time to do lots of searching?
I've never heard of a music player manufacturer ever openly describing their players as having a certain sound, only detailing what EQ options there are.
Have you ever listen to either Fiio X3 or X5?
If you have not, try audition them first and you will get the idea of their sound characteristics.