dts .mkv files play out of sync on my 2nd pc only

I have two pcs. The one in the living room is connect via hdmi to the HDTV then rca audio to the receiver and plays all my 5.1/dts .mkv file fine. The pc upstairs is hard wired by ethernet and is connected to a 22' lcd via dvi. This pc plays the 5.1 .mkv files fine but the dts .mkv files play out of sync. This pc is connected with 2.0 stereo pc speakers connected to the audtio port on the pc. Both pcs have ffdshow and hali splitter software installed. Can anyone provide some insight why these files are playing out of sync. Do i need an additional plug-in? etc?