No DTS from pc to tv (hdmi) and tv to amp (spdif)

Hi
my pc is connected to the LG32 inch LE4500 tv with hdmi cabel and i'm getting sound from my tv.I have connected the tv to my onkyo ht s3400 amp with fiber optic cable (spdif) but i'm getting only mono sound from it no DTS.All realtek drivers are installed from the dh67cl intel motherboard cd .What am i doing wrong?I've spent hours trying to figure it out but it wont work i even reinstalled win7 .before re install of win7 i was getting dts from the amp but it stopped suddenly.I'm a newbie at all this so please help .

Thank You.