Hi mate.
The PS3 needs to be set to LPCM and you need an amp that can accept this over HDMI to make use of HD audio from the PS3
which internally decodes all HD audio soundtracks.
Here's the heads up.
PCM
What it is: A PCM track is an exact replication of the studio master, encoded on disc without compression. The benefit to this is that it maintains the purity of the source without any loss of fidelity that may come from compression. The downside is that an uncompressed audio track takes up a tremendous amount of disc space, which may (especially on single-layer BD25 discs) negatively affect the video quality of the movie. While the Blu-ray format is capable of utilizing PCM audio up to 24-bit resolution, studios may choose to encode at 16-bit resolution instead, depending on the bit depth of the original source or concerns about conserving bandwidth (downsampling a 24-bit master to 16 bits is technically not the same thing as compression).
Level of support: All Blu-ray disc players are required to support PCM audio.
Examples of discs that use it: Almost all discs from Sony and Disney, as well as selected titles from Lionsgate and other studios.
How to get it:
Toslink or Coaxial SPDIF - SPDIF does not have enough bandwidth to carry a full 5.1 PCM signal, so the audio track will be downgraded to 2 channels only. This is generally an undesirable result.
HDMI - A PCM track can be transmitted in full quality over any version of HDMI and delivered to the receiver for D-to-A conversion and amplification.
Multi-channel analog - In this case, the player converts the PCM to analog and sends it to the receiver for amplification. The quality of the DACs in the player will determine the final audio quality. If the disc player has inferior DACs to the receiver, an HDMI connection is preferred.