Well, that sound issue with blu-ray movies is still driving me fucking nuts.
As Pdub mentioned, it does seem to be a conflict with the HDMI between the blu-ray and HDTV, and the surround sound system that's connected to the blu-ray player. But what I don't understand is, why in fuck's name do I get the 5.1 sound for the previews and intros (and even the blu-ray menu where you select the language, the bonus features, etc), and I get fucking nothing as soon as the movie starts?!!
I tried a bunch of different setups, I switched from optical cable to coaxial, I tried connecting the TV directly to the receiver with an optical cable, I changed the blu-ray player settings to HDMI-mute (which is basically supposed to stop the HDMI cable from taking the sound portion, thus leaving the optical cable plugged to the receiver do that job), and I get the same outcome.
I figured my receiver might be fucked and it may not decode the sound correctly, but then why the hell would it work fine during the previews/intros?
Not sure what to do anymore here...

EDIT: it looks like
this guy had the exact same problem. I'll try to install the latest firmware and see what happens for now...