Motherboard onboard audio to receiver?

Hey guys, I have the Asrock 990fx extreme4 motherboard. I also have a Harmon Kardon AVR 225. What's the best way to get 5.1 channel surround sound coming out of my receiver? The mobo has analog audio out 3.5mm plugs and the receiver has like-colored speaker channel audio-in plugs. 

What do? 

From your motherboard either spdif, which I believe is only 2 channels for the consumer version, or optical out, both are digital connections. It depends on you reciever's inputs. Choose accordingly

I just looked at your mobo, I would go optical (ADAT) out all the way. Located next to the spdif connection

Yes your motherboard has an S/PDIF output, and that gives a lot of flexibility, because there not only is a Toslink-style optical output, but there is also an internal S/PDIF connector, that you can use to connect it to a coaxial digital connector.

Only the S/PDIF output of the motherboard should be used, because it is a pure digital signal, everything else, as soon as it's analog, is sub par because the A/D converters and the pre-amp circuitry both suck and the analog audio path is compromised by EMI from the motherboard itself and the peripherals inside the case.

An optional easy audio upgrade is to get a USB sound card with a digital output and a DSP, like the Creative X-Fi 5.1 pro, which is not expensive, and the X-Fi DSP cleans up the sound quality of compressed audio formats incredibly well without adding noticeable latency. Any conversion will be done by the DSP also, so your CPU will have less load as a secondary benefit. The pre-amp circuitry in the 5.1 pro can be easily upgraded for a few bucks to mainstream audiophile spec, the mod is well documented on the internet, but as you'll be using a receiver, you only need to do that if you plan on using the direct headphones output with good headphones for instance, otherwise the optical output will connect to your receiver and you'll get incredibly good sound quality. The Creative X-Fi DSP system is arguably one of the best compressed audio playback solutions available today, even though the technology is already quite old: it's not just an EQ, it's also a dynamics processor, it increases the dynamics and the frequency response in an intelligent way, without adding bass or virtual bass, what most other systems do, and the result is a sound reproduction with great soundstaging and realism, even from mp3's or other compressed audio formats.

The other advantage of the X-Fi soundcards is that they have a very flexible output format selection, you can go from 16-bit 44.1 kHz all the way up to 24-bit 192 kHz, and the card has a selectable USB-bandwidth for that, in order to integrate it into a USB-chain easily. Normally the card will communicate with the PC over USB at high speed USB 2.0 spec, which is perfectly fine for most bitstreams, but you can switch it over to full speed, for high priority full duplex multi-channel super high resolution audio bitstreams. And it also just works with GNU/Linux, because it basically doesn't need software to performs it's DSP task, it's all done by an independant chip, and Creative X-Fi support has been part of the linux kernel since 3.2 or something.

http://www.newegg.com/Product/Product.aspx?Item=N82E16829997022

this is kind of what i'm looking for, but this is an extension. I'll continue this in the sound card area