there's just no way to make the guy satisfied no matter how, so burn in or not, he said he's returning the m23(also a lot of other craps, in his own words, i gather he's very picky listener then)
everybody's hearing is different, if the UA4 is better than m23, then who are we to convince otherwise. as this is the truth, for him.
good luck in searching a dap that suits your taste
@laleeee , i wish you a good journey.
back to m23:
for me, the m23 is superbb for it's price. i've had the m11 plus ess before and just from memory, the m23 has improved significantly from the old m11 plus ess! i also have the m15s, m17. the m23 earns its' place amongst it's brothers. also, to be completely honest, even when i first had the m17, the sound tuning of fiio take some time to get used to, it doesn't jump out in your face, it's very neutral and honest and very easily appreciated once you get it. and once you do, it is amazing!
a good sound quality is not the only thing i look for in dap, usabilty, bug free OS, price, also comes into factor. the one thing from fiio : the DESKTOP MODE. has been the unique point of their products. and i find it immensely useful on each every one of them as i hate and experienced battery degradation on devices which happened to my other past daps from various companies..