I think in music you will see that not many people (maybe none) use surround sound. First you have to have the drivers for it, and usually the drivers with an audio/interface like the AudioBox or about any one of those will be stereo only.
If only hooking up stereo speakers then an adaptor out of the audiobox will do.
http://www.amazon.com/Hosa-YMP-434-Female-8-Inch-Breakout/dp/B0010D0HO0/ref=sr_1_22?ie=UTF8&qid=1391277272&sr=8-22&keywords=stereo+male+to+mono+femaleFemale TRS 1/8" to Dual Male TS 1/4"
I would not necessarily buy a Hosa cable but I am sure a local electronics store has the same thing or perhaps even walmart - somewhere in your area.
Thus you plug your speakers into the single mini-plug connection just like a headphone because computer speakers usually have mini-plug stereo connections.
Maybe not elegant but it works.
I used to have surround sound but gave it up because stereo is usually what people use for music, surround may be for movies, but unless you are doing movie music and have much better equipment, the AudioBox will do all the music in stereo.
Up to you how you go.
The reason not to use Hosa cables is that with some equipment they can get stuck because as you see on the 1/4" Tips of the jacks on the cable it is more triangular than rounded and those tips (which carries the lead while the sleeve is the ground) get stuck in combination connections like on the front of your AudioBox - you do not want to use them there - you may break the connection or have to take the unit apart to get the cable back out. Use rounded cable ends on all equipment. The back of the unit is not a combination connector with the Main Outs so probably safe there.
Yes some people have got those Tips on the jack stuck in very expensive equipment using them on the front of a unit with a combination connector and they were not happy at all.