ac3 pass not working, need help to get 5.1

[jrterry1976]

I have Smplayer running on a W7 64 bit system using the HD SPDIF out on a Biostar MCP6P M2+ mobo with a 2.2GH AMD processor and GeForce 8400 card. The digital out is connected to the coax in on my receiver (pioneer VSX-516).The problem is, when I select AC3/DTS pass through under the audio tab in Smplayer, I get no audio and the player sometimes crashes. If I uncheck the box, I get stereo sound and no problems.I am sure my hardware is functioning because VLC player will play the same 5.1 files/movies and provide 5.1 sound. I also can use the test feature in device manger and each speaker works. Media Center in W7 also produces 5.1 sound when using my OTA tuner for TV. Can someone please help me resolve this problem? Do I need an audio codec? Is Smplayer sending the correct digital stream to my receiver?