HDMI Vs. Optical Audio conections for PS3

[Meat]

I have recently switched my audio connections from my PS3. I had optical out to my A/V receiver and was impressed with its sound, however I learned that an optical connection cannot handle Multi or 5.1 PCM audio signals. After making the switch to HDMI, which does send the PCM 5.1 as I had hoped, I noticed that some of the Dolby Digital signals will not reach the receiver anymore. Some software, like a few demos, such as F1 and Tekken 5, do send DD 5.1 over or through the HDMI, however Motor Storm, the actual game disk, not a Demo, will not. Motor Storm used to be multi 5.1 with my optical imput, but is not multi now. It sounds like sound comes from my two front speakers only and not from the back speakers. Sound from back speakers is what makes that game cool. I also noticed this on some DVDs also. While I am playing a DVD or BD, you can display the audio/video information and change the audio settings for that BD with the audio button of the remote from PCM to Dolby Digital, when I do that some times Dolby Digital will not be multi 5.1. I checked the settings of the PS3, the correct audio codecs are selected under the HDMI setup area. I am curious if anyone else has noticed this and if you have an explantion or solution. Sony support was little help.

Thanks