Audio passthrough mode questions

I have the WD TV HD Media Player.  (It’s gen1, but I don’t think that matters here.) 

The support for Dolby Digitial (by which I assume they mean AC-3) is described as (paraphrasing) “Decodes to 2 channels only.  If there are more than 2 channels, the audio is passed through to the audio receiver.”

I have a few questions about this.  In audio passthrough mode, is the audio passed through both the S/PDIF port and the HDMI port?

Under what specific circumstances is the passthrough mode in effect?  Is there a way to influence when passthough mode is in effect?

Is there a way to turn off audio decoding?  I have an audio receiver, connected to the S/PDIF port, so I have no need for the WD TV HD Media Player to do any audio decoding.  I *only* want passthrough mode.  Can this be done?

The problem I’m having is that I have a MKV file with MPEG-2 video and (6-channel) AC-3 audio.  My receiver (which supports both Dolby Digital and DTS) is telling me that it’s receiving 2-channel PCM 48kHZ audio.  This is not what I want at all (in fact, it defeats the purpose of having an audio receiver).  How do I force the WD TV HD Media Player (again, gen1) to passthrough the original AC-3 audio to the audio receiver (via the S/PDIF port)?



Audio passthrough must work with both, HDMI and S/PDIF…

When you set up the audio output to: DIGITAL and connect with this cables to a receiver with DD/DTS decoder it woun´t downmix audio to stereo…