Surround sound from pc to receiver

Not sure of the best place to post this i have a MSI p67-ga45 motherboard
with realtek alc892 chipset. right now i have it hooked up to my older yamaha
receiver with a toslink cable which is great but i don't get surround sound in
games. if i understand correctly if i buy 3 sets of 3.5mm to rca cables
i can port the sound to my yama and let it decode it, it does DTS and prologic 2
good unit just does'nt have Hdmi inputs.i just wondered if this is the best easiest
way to go about this im not a audiophile but i don't want just stereo in games either.
will this work or will i have to buy a xonar or SB card don't really want to but i will
if it's necessary. there is no driver or anything that im aware of to get DTS from optical
in games which is silly because movies are fine.

thank you all for any help.

unless someone has a hdmi reciever for cheap lol i could get the sound from my hdmi from
my 560 ti so i guess thats a third option