1. Fiio X5 III DAP
2. Android 5.1.1 (customized by Fiio)
3. 2x AKM AK4490EN (32bit / 768kHz
Fiio claims that they have "deeply customized" Android audio system architecture (probably marketing jabbering for their custom music player APP?). Hopefully that doesn't hinder you from adding highres playback support to Poweramp for those devices.
audio_policy.conf