If you have the older "fat" PS3, set Audio Output Settings under Sound Settings to be HDMI and ensure all the relevant Linear PCM settings are ticked for 5.1. Then, under Video Settings, set the BD / DVD Audio Output Format (HDMI) to be Linear PCM. Your PS3 will then decode the HD audio soundtracks to PCM and you'll be getting the best audio.
If you have the newer PS3 slim, follow through the Audio Output Settings wizard in the same way i.e. selecting HDMI, but under the Video Settings, set the BD / DVD Audio Output Format (HDMI) to be Bitstream. Since the new slim version can bitstream these formats, your Samsung will then decode the HD audio formats and you'll be getting the best audio.