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I made use of Poweramp, foobar2k, player pro, Usb player pro, Neutron MP, Aimp, Hiby and Onkyo HF as the best sounding music players (from much more options) with my Fiio Dap and S8 with USB audio cable and balanced for IEM's with and without portable amp.
I choosed Onkyo HF paid version (a little expensive maybe, but for me worth it) for audio quality even if the parametric Eq from UAPP and Neutron are better (no need of Eq right now) the UI is simple and not too much configurable. If USB audio quality is the most important for you then Onkyo HF is a good option.
Hiby is good, I only make use of Sibilance reduction, but give me some errors with both Dap and smartphone. Sound quality is nice.
Want to know an opinion about S10+ and G8 ThinQ or incoming new alternatives.
Don't buy S10+ for sound. G8 would be better option for sound.