2.0 audio from PS3. HELP!

[Terd]

1st, I'm sure this may have been addressed at some point by someone, so I'm really sorry if I'm being a noob. I searched different threads for about 25 minutes but couldn't seem to find the specific answer to my problem.

Thanks in advance for any replies and help.

Here's my setup. I've got my PS3 running HDMI into the TV, and optical into the RCA receiver, that has no HDMI. I've got my PS3 audio set to "bitstream", and I watch movies in 5.1.

I've watched Terminator 2, Kung Fu Panda, The Dark Knight, The 5th Element, Black Hawk Down, Indiana Jones KOTCS, Batman Begins, and Iron Man, on BD without any problems. However, Wall-E, Alvin and the Chipmunks, and Prince Caspian all give me 5.1 audio on the previews and main menus, but as soon as the feature begins, all audio drops out completely. For me to get audio back, I've got to pull up the PS3 menu and switch my settings from "bitstream" to "linear PCM" which then decodes the audio as 2.0 pro-logic simulated surround stereo .

So my question is, is it the way Disney is coding their movies? Is there anything I can do? Am I missing something? Has anyone else heard of this, or had this problem? And most importantly, what is the most cost effective way of fixing this issue? It just seems wierd that I get 5.1 on previews and main menus, but silence during the feature.

I'm baffled