I have a sound problem. My system is connected like this:

A PlayStation 3 connect to my Philips 47PFL6907 TV using HDMI.
A Sony Dolby Digital receiver connect to the TV using SPDIF (optical).

When the PS3 sends 2 channel sound everything is OK.
Sound on both the TV and through the receiver (showing "Dolby DIgital 2.0").

But when I use programs that send 5.1 sound on the PS3 then:
Sound on the TV, and the receiver displays "Dolby Digital 5.1".
BUT there is no sound at all from the speaker on the receiver :-(

What could be wrong?
The TV has obviously detected the 5.1 sound input from the PS3 as it signals the deciever to change to 5.1.
But why isn't there any sound from the receiver?

Have tried all setting on all components without any result.
Only thing that helps is forcing the PS3 to send 2.0 output.
But then I get no surround sound in games or from DVD/BD :-(

I can of course connect the SPDIF (optical) directly from the PS3 to the receiver.
I know that works. But then I can't get any sound from the TV to the receiver.
And I get problems with the video delay (TV usually compensate for that).

I had a Philips TV with coax digital out earlier, and that all was OK.
Anyone have any idea on what couød be the problem now?

PS! Even stranger; if I watch a TV channel transmitting 5.1 sound THEN there is 5.1 sound from the receiver.
So I is only when the TV should forward 5.1 sound that the problem occurs.