Best Hdmi Receiver How Much Better Does An Hdmi Receiver Sound Than One That Only Goes Up To Optical?

How much better does an hdmi receiver sound than one that only goes up to optical? - best hdmi receiver

I have a PS3, so I'm really in HD. I am currently with an optical receiver, mounts (I use) and play games and movies in Dolby Digital 5.1 and DTS 5.1. How much sound better, are in an HDMI receiver? Thu PCM 5.1? I hear PCM sounds good, is it true? Can you give me some good (not much, I'm a student) I can see the devices?