It's a limitation of Android 4.4 and earlier that all music audio (everything except DTS/AC3/DTS-HD/True-HD with video) is downgraded to 44kHz max.
That goes for output via HDMI or S/PDIF.
This limitation is removed with Android 5.1 and later so the new Himedia products will support passthrough for up to 192 kHz 24bit audio (FLAC etc).
Should add that 192kHz audio can be played on H8 using many apps but it will be passed as 44kHz.
But H8 octa runs Android 5.1, so theoretically it should be possible to do it.
I don't have flac files, so I can't test it and I'm not familiar with the Kodi music player.
Is there a possibility with the Himedia custom Kodi music player with "passthrough" like in the video player or does the Kodi music player always perform a down conversion?
... Another untold story when moving media players over to Android.
This was done too quick and too early. Lollipop is a real improvement but still not perfect.
You are absolutely right, these are the drawbacks to use a telephone/tablet OS for media players.