How do you connect your iMAc to surround sound?

I have looked through the threads here ENDLESSLY!!!! And I, unfortunately, still seem to be at a loss on what to do.

As of right now, I have a headphone output going to the Red and White RCA analog to my surround sound input just like the ones here
The headphone male end is going into the very far left headphone jack of my iMac. I have a 5.1 surround sound system and I know that this isn't being used to it's full potential.

I am not fully sure on what to do with the Audio in / optical audio in port... If I connect a fiber optic cable to that into my digital input on my surround sound, is that all I need? (this?) No RCA plugins or anything....?

Also, I have read endlessly on the FireWave and I am not really sure what the point of that is...? I don't know how it comes into play with hooking up my surround sound system to my iMac.

I have the Sony HT-DDW670

Thanks guys, I'm a newb here too btw.

Cave Man said:

Get this cable and Plex and you're good to go. Also, have a read on surround sound for the Apple TV, which largely applies to Macs (but with Plex, it's even easier). Next you need content encoded in surround sound.

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So all I need for sound purposes is the TOSlink cable going from the optic out of the iMac to my Surround Sound System?? (cable wise).

Cave Man said:

Yes, your Sony receiver has one digital optical input. That's where the cable goes. The audio-out port on your Mac is dual-function analog and optical digital. The length of the optical plug is about 1/4" longer than an analog plug. That extra length activates a switch on the port that tells your Mac you've connected an optical cable. You can now use Dolby Digital (Quicktime/Front Row/VLC/Perian/Plex) or DTS (Plex, maybe VLC) digital audio up to 7.1 (although your receiver can only decode 5.1).

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So where does Plex come into play? Do I have to have that open in order to get the 5.1 sound? Or can I just keep it closed?

Cave Man said:

Getting Dolby Digital to work on a Mac can be challenging, even with Perian installed. DTS is even more difficult. Plex handles all of these codecs internally (i.e., they're not OS resources), thus it is nearly perfect for the playback of such content. If you don't use Plex, be prepared for some frustrations getting your system working smoothly.

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Thanks for the help, but this all seems too simple. If this is all one needs to do, then what's the point in the FireWave?

DoFoT9 said:

i just used the cable adaptor that came with my Logitech speakers, surround sound works like a charm

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What kind of adapter..?

Cave Man said:

If you already have that Sony receiver, then you really need to go with digital optical from your Mac. Don't waste your time or money on analog solutions. Seriously, the Toshiba cable is less than $3. How can you possibly go wrong?

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You're absolutely right