According to a report over at Bit-Tech AMD's newest 785G chipset is not capable of true HD audio. This is not to say that the quality level is not there but rather the number of channels. For True HDMI 1.3 HD Audio you need to support a full eight channels of sound yet the 785G only supports six.
The big problem now is that this puts the 785G behind both Intel and nVidia in this area. Intel and nVidia have had the full eight cannels for 7.1 surround since last year.
The lack of this particular feature from the 785G is an issue because most websites were lead to believe that a more complete feature set was present. As it stands there are very few sites that dig into the full audio functionality covering all angles from the board. So this one could slip by in the wash until the HTPC audiophiles caught it and complained.
AMD has admitted the lack of 7.1 support but did not comment further. Of course their recent campaign is aimed at mid-range users so they can spin it by saying "the average" user would not need that and "a real enthusiast would have a discrete audio card" both of which are very true, if only a little misleading.