"Nvidia GTX 260 video card connected with a SPDIF cable from SPDIF connector on motherboard to the video card"
so you are connecting the computer to itself? why?
take the cable off and export video and audio via the hdmi output on your soundcard. this takes your soundcard out of the equasion but your receiver does the processing instead. the default sound device will show up as either hdmi, your video card or in my case my receiver gets listed. i use this method (although i need a dvi to hdmi cable).
the other option would be to export video via the hdmi and to connect the spdif from motherboard to receiver for sound. however, since you only have an integrated soundcard i dont see why you would possibly want to do this. you might possibly have issues with setup if you go this route.