Con respecto a si puede hacer passthrough de audio en HD dejo un extracto de este enlace de Kodi: Settings/System - Kodi

"If you have a "capable receiver" option enabled that your device does not support then this will result in poor playback of video typically with a very low frames-per-second and no audio, so for example if the TrueHD capable receiver option were enabled then make sure that the playback device can passthrough TrueHD and that the connected device can decode TrueHD, if either of the devices do not support TrueHD then the TrueHD capable receiver option MUST be left disabled."