x RELIC x
Headphoneus Supremus
It's just a code referring to the hardware version. If I remember correctly, Fiio changed the RAM they were using between production runs.
In general - I honestly don't know what the fuss is about. People go crazy over fw versions with claims of sound changing, speed etc, etc. Guess what - my X3ii plays music. It has done from day one. It has maybe glitched twice in all the time I've had it. Most of the time I don't have the screen on - so I never notice lag between music playing and art changing. And it's not an iPod UI - but it has better hardware (decent line out, DAC function, decent EQ, digital out) - and it's only $200. There are trade-offs between different players. Half the issues are when peopel expect a $200 player to match a $800+ one.
I'll also add that the other half of issues are when the DAP isn't tied to a closed environment like iTunes to take care of the heavy lifting and with limited format support by Apple and no option for user formatted card options from third parties. The expanded format support and open system means that a few good practices need to be adhered to by the user, which are well documented by FiiO.