I have my hands on an alpha firmware for the X3. Alas it really is an alpha feature-wise: no EQ, no high gain setting, some other menu items missing, system settings that are in Chinese no matter what language you select (and the language selection is also missing from the menu so the only way to select language is the language selection screen that comes up on the first boot-up after flashing). But it is using the new UI, and seems to be using the new mp3 decoding engine. And gapless really is gapless (tested with Pink Floyd's DSOTM, FLAC) Who knows, it might even play DSD
If anyone wants to try it, they can pm me for a download link. Please, no redistributing the alpha and only report bugs to me via pm.
Edit: just received an updated beta of the firmware with EQ (both software 5-band and hardware 2-band), complete menu in English (although I note that the tag for "idle power off" and "sleep" have been mixed up), language selection in menu... all in all I'd rate this as a solid "beta" worth trying out and I anticipate to be inundated by pm requests so here's a public link
:
https://www.dropbox.com/s/wp5bs1j5gc06q0r/x3%20FW2.14beta.zip
Extract x3.fw into root folder of mSD card in X3 (that's formatted in FAT32), turn off X3, make sure X3 is adequately charged, hold down upper left menu button while pressing power key to start the update.
If things don't work out for you with the alpha here's the version 2.1 firmware to revert to
https://www.dropbox.com/s/d49q7vmdkhfeqjc/X3_FW2.1_EN.zip
I'm opening a new version of firmware for this in the bugzilla
https://app.devzing.com/FiiO/bugzilla/
although I anticipate this version to remain current for only a week or two at most