L/R SPDIF to Stereo, LS/RS to analog audio jack...

I have a number of DTS encoded audio files. Curently I use the SPDIF to run a signal to my Cary 3030/200 for the D/A conversion. I do this for a number of sources, Blu-ray, HD, DVD via a switch box that handles HDMI and SPDIF. It is issues with my home theare PC that I am hopingto find a solution for. Its an asus a3ion deluxe. It runs the realtek audio manager. For the rear channels i runthe analog audio out form the PC to an older reciver to the back channels. However with the PC I have to chose a default audio out put(SPDIF or Speakers). When its in spdif i get 2 ch form the stereo only. When i run it as speaker default i get only the rear channels. Id like both front and rear channels at the same time for 4ch sound as i do with the dvd players.
Seems to me that the dvd players dont turn off the output to the rear analog or spdif. Ie decodes to all outputs simaltaneously.