Not true. I think you sort of reading too much into FiiO's reply. There won't be any new feature on the international version of X5III besides the fact that the international X5III will have Google service running on it while the Chinese version won't (*because all Google server access are banned in China, so there is no point running them as they won't be able to connect to Google). There is only one reason why FiiO is selling the X5III in China first, because they know the Chinese consumers are more tolerable and patient of bug-fix, where the Western consumer (or at least some of them) ain't nearly as much - and they can get very vocal when they didn't have all their demand met yesterday (just read through the FiiO M3 and X1-II threads and you'll see). Thus FiiO has decided to release it on the Chinese market first, then get as much feedback and bugfix as possible before releasing it internationally, hoping that by the time when X5III hits the international market, it will at least be stable enough and won't get criticized as much.
Any apps that outputs sound on X5III will use the exact same DAC as the FiiO music app. There is no such a thing as an 'inferior sound chip' on the SoC. The problem is, In normal Android, Google has implemented a simple SRC (sample rate convertor) into the audio driver that will degrade the sound quality on any sound that isn't natively encoded into 16/44.1. But on X5III (as well as X7), FiiO has rebuilt the audio driver from the ground up so Android no longer degrade the SQ. In theory, whatever apps you choose to use should give you the same SQ as the FiiO music app.