I have my PS3 hooked up to an older LMC-1 pre-pro using the optical audio cable (no HDMI on the LMC-1). I read the huge thread on this board as well as a few other places that the proper audio setting is to use bitstream, so that the PS3 outputs a downmixed DD or DTS audio stream to the pro-pro.

I haven't had a problem watching 5-10 DVD's and BluYay disks since I got the PS3, until watching Planet Earth last night. There was no audio commentary, because I was getting no sound from the center channel. L/R and subwoofer were working fine. My pre-pro was showing that it was receiving a dolby signal, and I believe the only soundtrack on the Planet Earth BluRay is a 5.1 DD track anyway, so does anyone have an idea as to why I didn't get any sound from the center?

I ended up switching to LPCM, which only gave me 2.0 sound. But at least I had the commentary.

I would try setting the PS3 to LPCM and then set your pre out to 5 channel stereo and see if that sends the sound to all of your speakers.