Change the PS3 setting to PCM or Bitstream, see what happens + the PS3 has (somewhere) a setting for changing audio outputs via HDMI, so that could be it & mostliky that is set to PCM but for you it sould be bitstream.
I just got the Sony 910 receiver and I have the PS3 hooked up with HDMI. I'm a little new to this, I had an old Sony 5.1 with no problems. But when in an HDMI connection I can't get anything to work correctly. Neither Dolby Digital or DTS will display when playing a compatible DVD (only sound it coming from front 2 and center.) As well as no options such as PLII, PLIIx etc are given, when the "AFD/MOVIE/MUSIC" buttons are pressed it says "Not Used." However all seems well with optical. Any help is appreciated. Thanks!