The truth is the studios did not want to update the S/PDIF specification, an unencrypted interface, to carry the new codecs. So it was mandated that they only be sent over HDMI.
Interesting information about that decision.
And thx a lot for your help.
My PS3 was in fact configured for bitstream at start. But because of Black Hawk Down movie soundtracks, I was trying different ways to get the better of this and from my actual equipment.
Got over 50 high def movies, but only 2 of them have PCM 5.1 soundtrack. At least they also have DD 5.1 !