I have an AMD E-350 system (Radeon HD6310).  When I connect it directly to my
receiver and play a file with AC3 audio, the receiver properly switches over to
Dolby Digital decoding.  However, when I connect the HDMI to another device's
pass-through (Vizio TV, Xbox One), the receiver stays in stereo mode and I get
garbage audio.  Other devices can send Dolby Digital through (e.g. I tried a
TiVo Roamio through the Vizio TV), so I know it can be done.

I'm guessing there's some bit of HDMI handshake not happening when the Radeon
tries to switch modes and is connected to another device, but I don't know how
to debug that.  Please let me know what I can do to figure this out.

I'm testing this with a trailer downloaded from hdtrailers.net, playing with
either XBMC or VLC.