AV Receiver won't play audio from pc

I've read that this is a common problem but have yet to see a reason or solution. I have a little Lenovo Ideacenter i'm running as my media pc for downloaded, streamed or ripped movies which is connected to a Yamaha HTR-6140. I'm using the HDMI output but if I run it through the receiver I don't get any sound but if I hook it directly to the tv the sound works fine. I have hooked the TV (Samsung UN40C7000) hooked up to the receiver via optical cable which is working but looking at the display is only showing L R speaker configuration unlike when I play bluerays through the PS3 (connected directly to the receiver) that have all the speakers shown and actually sounds like a surround system and not just a 5 channel stereo output. Any ideas?