Coaxial and Optical

Dear Brothers,
i have a xbox 360 which have optical output, but my 5.1 only have coaxial input. is there any way i can use my 5.1 for the sound of the xbox? what do i need and how much will it cause? (cheapest please)

Dear kk_ho,
do you mind telling me roughly how much those you mentioned will cost me? because if it is too expensive, i may just stick to the TV sound.
and will you stay at the hififever office on Sat?
thank you again.