Since I dont have a dolby digital decoder in my home reciever and just dolby prologic couldnt i get the optical cable and send the digital decoding out from the sound card in the computer into the home reciever for two channel mode standard stereo setting and turn it into a true digital 2 channel stereo reciever? (any thoughts) I mean a dolby digital sound card is only 15 bucks
That probably would work; but what's the point? You've just swapped one set of DAC's for another. Newer DAC's possibly? Everything has to be converted back to analog to make anything work with your present receiver. I guess one of us is not understanding what you mean by "a true digital" receiver.
If you found a Dolby digital sound card which had 5.1 analogue outputs (they do exist), and if your receiver has 5.1 multi-inputs, then it would be worth doing and you'd get full discrete 5.1 channels. In effect you'd be using the receiver as an analogue amp.
But the receiver must have 5.1 inputs, which is unlikely.
Best Buy has their house brand receiver on sale for $99. I believe it will do everything you want as far as decoding goes. It also has pre amp outputs to enable a different, or better, amplifier to be used with the receiver as a processor. I can't speak to the quality, but for $99, you can just throw it away if it breaks.