They're both
fine. The older K5 Pro ESS is a bit
rustic but would go a bit louder single-ended (with also marginally higher noise floor), although both would be plenty loud enough for a HD560S and noise wouldn't be an issue for either.
K11_parameters
www.fiio.com
K5PRO ESS_parameters,FiiO--Born for Music
www.fiio.com
Note: 12Vp-p = 4.2 Vrms, 24.5Vp-p = 8.6 Vrms.
Among all 3, I would probably pick the K11. The DX1 would have some advantages for driving high sensitivity IEMs with its low gain mode and very low output noise.
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