I just recently posted about how to do this. If you have any Mac that's from 2010 or later, you can actually send multichannel HDMI out from your Mac with a simple Minidisplayport to HDMI adapter (from your signature it appears you have the current quad 3.2, so that will definitely work).
I only recently found out about this capability. Basically the HDMI protocol is built into the recent Macs, even if they don't have the physical HDMI output jack.
To verfy that your Mac has this capability, go to the upper left Apple icon, select "About this Mac">"more info">"system report">"hardware">"Audio (built in)". Over to the right you will see all your Mac's options including line out, headphone out, digital out, etc. Down at the bottom you will see "HDMI / Displayport output". If that last thing is listed, then your Mac has this capability. You just need the adapter and cable and you're good to go.
What you'll be doing is sending multichannel PCM audio out. Most recievers will accept that. No need for encoders/decoders, etc.
This is the adapter you need:
http://www.bestbuy.com/site/DisplayP...port&cp=1&lp=4
Amazon has it even cheaper, and you can just have Best Buy match the price (sometimes they'll calculate the match with shipping added):
http://www.amazon.com/gp/product/B00...A1C9SLS6HT1I6Z
And of course you'll need an HDMI cable of whatever length you need.
I've been using this from my 2010 Mac Pro into my home theater receiver (they're both in the same room). With a single HDMI cable, I not only get the multichannel audio, but my TV (hooked up by HDMI to the receiver) is seen by the Mac as a 2nd display, where I have the typical options of using it for extended desktop, or mirroring mode, just like I would with any other display.
So as not to waste more space, I will link to my original posts where I describe how to set this up:
http://duc.avid.com/showthread.php?t=341812
Let me know if you have more questions about it.
Note that I have not said anything about using optical cables, because I briefly tried it and was not able to get it to work.
But theoretically, you should be able to just go into your reciever's optical inputs, and the same principle applies, in that you're sending straigh PCM out with no need for encoding/decoding. So all you should need is an optical cable.
I have a cheap reciever, and I did not spend much time trying to mess with it. When I couldn't get it to work, I decided it was more convenient the other way. But your experience may differ, so it may work better for you.
I like the fact that using the HDMI from the Mac also lets me use my big screen TV as an additional monitor for the computer as well.