than full Dolby True HD or DTS-HD MA audio but still better than lossless Dolby Digital or a DTS signal. Pptical cables can carry higher bandwidth signals than standard DD and DTS so the uncompressed codecs will down-rez the signal only as much as necessary. The difference you will hear between your existing system and a new HDMI receiver will be quite subtle.
The main difference I hear between lossless standard digital codecs and their lossless breathren is greater dynamic range (sometimes shockingly so). But I have to admit that with some movies its really hard to tell the difference, even on a nice system.
I have a Yamaha HRE-5760 with no HDMI cables, Celston speakers and a Samsung BD-P1500 blue ray. Blue ray is hooked up by hdmi cable to tv and a fiber opic cable from tv to receiver. Blue Ray is hooked up by optic cable to receiver. I have a 7.2 system and it does sound pretty good when playing a movie. Would an uptodate receiver give me better sound with all hdmi cables, or would I be wating my money getting a better reciver?