Also just to say that I have now sold both the F805 and X3 in favor of the iBasso DX50. The DX50 seems to be a cross between the F805 and X3 in that the resolving mids of the F805 are combined with the musicality and soundstage of the X3. It is not perfect but then nothing is!
I recently went to London and had a chance to try the DX50 with some Sennheiser HD800, B&O H6, Denon AH-D600 and Philips X1 headphones. I have to say I was incredibly impressed and the DX50 performed admirably and gave me the confidence it can drive pretty much anything with ease. With my Westones it performs brilliantly, probably have to spend a lot more money to beat it! :)