I bought both dx50 and x3 and kept the X3.
I won't pretend that it should be everybody's choice but from my point of view it was simple to pick the x3:
dx50 had very slight but audible noise on my jh13. and I really hate noise on my daps. the X3 sure is better on this.
I'm not a fan of tactile.
there is no difference between HO and LO's volume. some will be happy to have volume on the LO. but to me it is a sure way to kill my iems and my ears every time I go back from the LO full volume to the HO.
I have real use of the balance setting for intras I can't fit perfectly (not going deep enough). the balance helps me get the voice back at the center and an overall better imaging. I don't need any balance on customs, headphones, and iems reaching the 2nd bent so it isn't a must but a nice feature to me so I can consider some good sounding IEMs with bad fit.
I actually really like the EQ on the X3 as I don't hear the usual distortion of say my cowon's EQ. less options for better quality, I can go for that.
I preferred the form factor of the X3. the dx50 is larger and bigger and didn't feel as good in a pocket.
I believe I can break both by sitting on them so no winner on sturdiness.
the good stuff for the dx50 IMO:
wider and higher soundstage (but not much depth) you get the usual imaging of headphones when the X3 puts a lot of what is usually above right in front of you and has an impressive depth to my ears (more like a home stereo).
the screen staying off when you press next or pause.
more battery (my comfort zone is 13+hours for a dap so the X3 is a little short for my uses)
I can't talk about any firmware related features/bugs as both companies have work to do to get out of the beta feeling.
about sound I didn't spend much time on the dx50 (hiss is a bummer) but I'd say less bass and a bit more natural mids for the dx50. on some iems I have to raise the trebles to get the voices how I'm used to hear them on the X3. there was something harsh in the trebles but it might get away with time.or not.
anyway I kept the X3, and if the X5 has a little less power (getting pretty hot on my jh13) but can pass 15h I will go for it as soon as you make it available.
and I appreciate the open dialogue james had with us this all time. it is something I value and on the other hand I really disliked the silent treatment by ibasso.
I really believe this long nightmarish soap opera about the X3 for years now, have brought a very promising start for fiio in the dap industry and the good LO, low impedance, big power amp combo is something the likes of sony and iriver should take example on. just saying ;)