I have found the following workarounds to play MKV files with 5.1 AAC audio. AppleTv has not got a device to actually play 6 channel AAC however it should be able to down mix to 2 so that the signal is picked up by a Dolby Pro Logic processor. This however in 9.11 does not work through optical output.
Option 1: before playing the file go into Settings-System and set downmixing multichannel to stereo one. This option has to be set on before playing your file because the equivalent audio option that you can recall with the context menu won't work and the audio of your receiver will completely be switched off
Option 2: connect two RCA connectors and disconnect the Toslink
Option 3: use HDMI audio and disconnect Toslink
There is clearly an issue with the implementation of downmixing as in 9.04 AAC files would still not play multichannel but XBMC would force downmixing on its own
Hope this helps while the bug is ironed out
Option 1: before playing the file go into Settings-System and set downmixing multichannel to stereo one. This option has to be set on before playing your file because the equivalent audio option that you can recall with the context menu won't work and the audio of your receiver will completely be switched off
Option 2: connect two RCA connectors and disconnect the Toslink
Option 3: use HDMI audio and disconnect Toslink
There is clearly an issue with the implementation of downmixing as in 9.04 AAC files would still not play multichannel but XBMC would force downmixing on its own
Hope this helps while the bug is ironed out
