Mmmmh Coffee. My powere was out this morning so no shower and no coffee. Lots of hot water to get cleaned up from our propane stove top but instant doesn't do it for me.

Anyways, now that the caffine panic is over.
I really think I am sending you on a wild goose chase as you say that you do get 5.1 from DVDs but your last statement made me think of this. Here is the quote that I read regarding the TV HDMI cable sending back a return signal demanding to only have stereo. Note:I can't confirm this to be correct, just that this one spot on the 'Interweb' says its so.

If you are using an HDMI cable in LPCM mode, your television reports the native format it outputs in to the PS3. Since the television outputs in 2ch surround sound, it will tell the PS3 that and the PS3 will refuse to send anything more than that. That prevents double processing of sound.

Audio selections are found in two places and can be very confusing because you think setting one spot is enough but combinations can do different things. The first possible spot to find audio/port options is where you expect to find it...
PS3 --> Settings --> Sound Settings --> Audio Output settings.

Here is a link that explains the choices better than I can.
http://manuals.playstation.net/document/en/ps3/current/settings/index_sound.html

The other, less obvious spot, is under
Settings --> Video Settings ->> BD/DVD Audio Output Format (HDMI)

Its covered near the end of this page.
http://manuals.playstation.net/document/en/ps3/current/settings/bdsettings.html#1470


The TV return signal, if it is true, sounds to fit exactly your symptoms of the PS3 recognizing a dolby signal but not outputting it. I'm total HDMI A+V to the receiver and HDMI to the TV so I couldn't verify my settings for you as I wouldn't experience the same issue in this config.



With great power comes Awesome irresponsibility.