Optical vs 3.5mm jack In MY case?

it's really just a regular ALC1150 chip with some ASUS software. Marketing at it's best.

why not try both and go with what sounds better to you in the end?

Definitely 3 x 3.5mm cable. Most PC audio is uncompressed LPCM and optical cables can only transmit LPCM in 2.0 due to having a very limited bandwith (1.5mbps) -> if you connect via optical you're only going to get stereo sound.

Looking at your specs on those speakers, I would try the optical cable because your speaker only has one 3.5 mm input jack. Although you could try the 3.5 mm jack just to see what happens.

I don't know what the previous people are smoking but those speakers have both optical and coaxial SPDIF inputs and both will accept the same 5.1 signal from your motherboard.

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Incorrect, an optical cable is incapable of transmitting 5.1 PCM audio due to bandwith limitations. If you try to send a PC's audio over an optical cable it will be automatically downmixed to 2.0.

To clarify: An optical cable can transmit compressed 5.1 audio - think: Dolby Digital or DTS - but PCs do not use DD or DTS, they use uncompressed, high bit rate PCM audio.

So a PC cannot transmit 5.1 dolby digital over optical TOSLINK SPDIF? You are right, sort of.

A sound card or onboard sound with Dolby Digital Live or DTS Connect is designed for sending DD or DTS 5.1 over optical connections. Without those then it's just 2.0. The receiver must have a dolby digital or DTS decoder.

I checked and your motherboard has DTS connect but no mention of Dolby Digital Live. So you could use that. You logitech speakers have a DTS decoder for the optical input so yes it would work.

The reason many people used to purchase soundcards in the past was to get Dolby Digital Live to be able to transmit 5.1 over the optical S/PDIF to a home theatre receiver that doesn't have the 3.5mm or analogue inputs. In your case it would work but it is more of a hassle than just using the analogue 3.5mm inputs.

So a PC cannot transmit 5.1 dolby digital over optical TOSLINK SPDIF?

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That's not quite what I was saying. My point was that by default a PC produces uncompressed PCM audio, and a PC cannot transmit 5.1 PCM audio over SPDIF (optical/coaxial).

I didn't bother to mention DTS:C or DDL because compressing the audio into DTS then decompressing it again at the other end means a double loss of audio quality, but using the 3.5mm cables means full, uncompressed audio is sent.. The only context in which DDL or DTS:C makes any sense is when you only have SPDIF connections and no option at all for analogue or HDMI, which wasn't the case here.

Actually this Motherboard does support DTS output. My speakers are on the way and I'm gonna test them as soon as they arrive.

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To condense the main points that were discussed above:

Optical cables have low bandwith and can only transmit low quality, heavily compressed 5.1 audio. DTS is a common type of low quality, heavily compressed 5.1 audio (the other most common one being being Dolby Digital).

PCM is high quality, uncompressed audio. Your PC uses PCM audio by default. PCM audio can be sent to your speakers by using 3x3.5mm cables that will be included in the box with your speakers. (FYI PCM audio can also be transmitted via HDMI, but your speakers don't have an HDMI input, so irrelevant here, but I'm mentioning it for completeness).

The optical and coaxial inputs on your speakers are there so you can connect other devices such as a TiVo or games console.

To sum up and makes things clearer.

- The optical or Coaxial (both S/PDIF outs) can only transmit a dolby digital or DTS signal which must be decoded by your speakers or home theatre receiver.
- Your speakers have both decoders so your fine
- Sound cards can only send a dolby digital (DD) or DTS signal if it has DD Live or DTS connect features....your motherboard has DTS connect for sure and possibly DD Live
- People who have home theatre receivers with an optical in often buy soundcards with DD Live just for this feature
- You will have less problems if using the 3.5mm inputs as you don't need to play with the DTS connect settings of your motherboard sound
- When using the 3.5mm outs, the motherboard does all the surround sound decoding for you and sends it through the 3 outputs, and they are individually adjustable in the software....you may notice more 3d options and better gaming audio using the 3.5mm outs for this reason
- Your speakers are very nice computer speakers, but they are not a $5000 audiophile studio system, therfore you won't notice a sound quality advantage by using the optical out, the only real advantage will be the smaller optical cable as opposed to the 3 3.5mm cable bundle

I'd try both for fun and play around with your sound software to see if you notice a difference. Optical will use the DAC of the speakers, 3.5mm will use the DAC of the motherboard, so technically there is a sound quality difference. But, both DACs are around the same quality and your speakers arn't good enough to show the difference, and your ears probably arn't good enough to notice a difference.

Hi,
               For your info i had tried Creative Sound blaster Zx and Zxr for both 3.5mm and optical and both 3.5mm and optical using onboard sound chip Asus S1220 Asrock ALC892 Gigabyte Core3D.
               Speakers are simple Logitech Z906(SGD$600+ when i bought) Year 2011 Made and Panasonic SC-BT205(SGD$1300+when i bought)Year 2010 Home Threatre system(For my PS3 At That Moment aka ATM) Both are pretty cheap system compared to those professorsss in audio dealing in $5-6 digit crazy concert hall or mansion hall trumpet style Gamophone.
The results are as followed=
              Onboard creative core3d marketing bullshit 3.5mm custom hi-fi cables - Core3D was better than most Realtek ALxxxx quite a match with s1220 series on quality and clarity.
Onboard creative core3d marketing bullshit Glass fibre optical 2.5 feet - So much better than 3.5mm .First Movie .2nd Music . 3th Games.All just much better than 3.5mm.Quality and Hz wise just sounded clearer and much more in sync with my monitor 1ms in game no lag totally you hear it as what you see in game i could felt much in sync with the screen than slower 3.5mm.
              Creative SB ZxR and Zx - I borrowed it (ZxR) from the shop  After a 2 days trial i went back and purchased a Zx.I read alot comments commended by Unknown expert ,Not Certified Dr,So called Professor who don't try, trial,experiment or review but bluntly gave their answer out of their brain OH EARTH IS DAMN ROUND!!! GOD DAMN MADE IT ROUND! and i couldn't quite listen to it . So i followed my instinct as im very puzzled in the "Sound field" of a damn PC system .SO!!!!! Yes! 

                The 3.5mm by Creative ZxR perform much better than onboard Realtek ALC , S ,Creative SB Core3D and not to mention even better with optical from my opinion especially if you tinker tinkle winkle their SOFTWARE and IN MOVIE MUSIC GAME you could felt it sounded much better than bloody 3.5mm.Only analog cable i think better at playing music will be 6.5mm !!! For best 3.5mm in the whole wide earth vs optical, i would say take the fibre glass optical !!! Its better for game due to refresh time for sync with screen is much quicker than 3.5mm and movie!!! For music wise GREAT CUSTOM 3.5mm come close to optical however with software in my opinion if i custom i felt and i feel that optical is my pick . MOVIE GAME Optical is big YES over 3.5mm. Music depends on me and yrself!!! I just felt optical onboard and optical Creative without any touch on the software its already a clear better clarity!!! With the software the PCIE Creative is definitely Big Bang YES for the Game and Movie on optical over onboard! For 3.5mm wise Big bang on Movie Music Game PCIE Creative over onboard!!!

             I purchased the Zx in the end as i got nothing to buy that i need from the shop somehow I wanted to let the sales person earn some money . Mod the Zx to Black and green LED for my future build atm and i prefer less connection since ZxR optical is not on main PCIE slot card that is link to another sister card.

               The preference comes from the fact that the OPTICAL “light pipe” is totally immune to any electromagnetic noise you may have in your home, like wash machines changing cycles or air conditioners starting up. The transient electromagnetic noise generated by the home appliances can sometimes cause interference in the signal on the coax or USB cables which result in a short loss of sync with the source and thus a short music dropout (usually less than one second).
           Please do not be an expert that mix all Digital type connection!!! Optical is not like USB or Coaxial!!!

The preference comes from the fact that the OPTICAL “light pipe” is totally immune to any electromagnetic noise you may have in your home, like wash machines changing cycles or air conditioners starting up. The transient electromagnetic noise generated by the home appliances can sometimes cause interference in the signal on the coax or USB cables which result in a short loss of sync with the source and thus a short music dropout (usually less than one second).

You seems like an expert but sometimes you could not remember so many things correctly !This reply is just for you to get your facts right on Optical!!! Digital like Coaxial or USB is different from Optical Digital! Remember that well ! Expert!