The DX50 sounds great, and the built-in amp has the juice to power some larger headphones. I mostly use IEMs, but it has no problem driving my K712 and HE-400.
However, there are some annoyances that drive me crazy:
* No gapless playback. iBasso had this mostly-working in firmware 1.2.8, but broke it again in 1.5.0.
* No support for the "Disc Number" tag. If you play a 2-disc album, it plays Disc 1 track 1, Disc 2 track 1, Disc 1 track 2, Disc 2 track 2, etc. The workaround is to break the discs up and give them different names (yuck). Another workaround is to select the album directly from the file system; it plays the files sequentially, so if your files are named sensibly you're good.
* "Browse by artist" sorts by the "Artist" tag, not the "Album Artist" tag. Which means every artist in every compilation gets listed separately. Selecting Artist->Album plays ONLY the tracks with a matching Artist tag. For instance, if the album has some tracks tagged "Artist featuring Other Artist", they will be omitted from the playlist. The workaround if you like to browse by Artist->Album is to browse the folders directly. Or you can re-tag your files (yuck).
I sent 2 emails to iBasso in March asking about tagging/sorting issues, but never received a reply. From scanning the HeadFi threads, it seems these have always been problems and iBasso has always been aware of them. So at this point I don't expect a fix any time soon.