Just had a Fiio E10 that I purchased off of eBay delivered today, and I've been testing it all afternoon with my Westone UM3X while working at home.
I bought the E10 to use in my office with a pair of Sony MDR-V6, which always stay there. Can't wait until I get to the office on Monday to try the combination... but I have to say... the E10/UM3X combo is pretty damn good. The UM3X normally never leave my Rockboxed Fuze, but I wanted to test the E10 with something portable (my HD600 sounded pretty thin on it), and I'm sure glad I did.
Caveat: I use the iZotope Ozone Free plugin for Winamp ("subtle analog modeling" preset with "Tube Limiter" bypassed), primarily to add some presence. I know that the general consensus around here is against the use any sort of plugin, but I don't care: it has always sounded natural, and sounds especially good with this mini system.