There are several problems with the Realtek RTD1619 media processor and its SDK that Dune players are using. Here're some issues according to Dune tech support.
1. No audio from the back 2 channels for 4.0 quad audio.
2. No audio for several seconds when starting/resuming DVD playback
3. Downmixing all multichannel PCM to 2 channel PCM before passing it to Kodi app. I'm using Kodi for gapless playback since Dune internal player doesn't play gapless.