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Had my (secondhand, but mint) for a couple of weeks now and I am very pleased with it. It's played everything I put on the 64GB micro SD card and when I dug out an old OTC cable and a 64GB USB2 flash drive, that was picked up and worked immediately as well. No hangups or crashes. Only thing to note, I sometimes get interference (clicks or hums) if my mobile phone is anywhere near the DX50. First heard it when travelling on a train, just tried it again at home with 3g & wi-fi and there's nothing, maybe just the hint of a low hum. Strange Never had that with my old iPod 5.5, though..
Am using Sennheiser Momentum (on ear) headphones and it sounds great. Have my old LIttle Dot mk1 & a Mini^3 charging to see if an amp improves the sound, but I like the compactness of the DX50 on its own.
I tried this for a while and enjoyed the simplicity, but I was missing the bass boost that the C5 provides. After having the upgraded 3way bass boost switch installed on the C5, my DX didn't seem complete without it.