question about cheap systems

[-Sandro-]

Hello,
I have a PC with a gigabyte mainboard with integrated sound card, which has analogic 5.1 outputs plus coxial and SPDIF outputs.

I'd like to add a cheap 5.1 speakers system (around $100) just to have a surround sound while maintaining a discrete quality. Since I'm happy with my actual stereo Creative speakers I was looking the Inspire M5300.

For what I can see on the back it seems to have 1 analogic input (jack stereo I guess) and SPDIF. Now if it had analogic input I could simply connected them and reproduce any 5.1 audio I want, but in this case I only have SPDIF.
Now I don't have any experience with this (first time), what does it do? Does it send digital sound to the system in bitstream? If yes can it decode them? There's no information on the official site about it, if not does the PC decode any file and send them in PCM so the system can reproduce via SPDIF as if it was connected in analogic? I'm really interested in AAC and new DTS HD MA and Dolby THD