7.1 HD-Audio is unavailable using Kodi native player on all firmwares and versions of Kodi.
To get 7.1 audio (local/LAN only) you need to use Kodi+wrapper.
* How to check wrapper is installed? Run Kodi and navigate to Videos - Files - any video file. Press remote menu key. You should get a 'play using..' option with 'Wrapper' as an option.
* How to reinstall wrapper? Shutdown Kodi. Find wrapper app at My Apps - Wrapper. Select 'use Kodi player'. Exit wrapper app. Run wrapper app again. Select 'use wrapper player'. Exit wrapper app. Restart Kodi.