The software I have is an internal company tool, and basically has a decoder in it, but it does not do any breaking up of the audio and routing it to any outputs as you're looking for. It is a visual tool, that shows where the surround decoder would steer the audio. So in other words, If I had a surround mix that I did a circle pan in a surround setup and it was surround encoded down to a stereo mix. I would input that stereo mix into the software's inputs, and there is a visual display that would show where in a 5.1 listening environment that the sound would be steered too. So for my circle pan mix, it would show the display circuling around. So that's what my plan was to test out Vegas's surround to Stereo downmix, to see if it was truly a 5.1 encoder by creating a circle pan of pink noise in Vegas and then down mixing it. If it was surround encoded, the visual display would show the decoder playing back the original surround information. But as you saw Peter informed us that the downmix, is not a surround encoded algorithm.

Hopefully, that makes sense. I saw your original post and thought about this and I don't know of any software that does this. I have saw some software that contained a Prologic II encoder, but it was relatively expensive. The only way I could think of was to use a hardware device that supports either Dolby Prologic II or Logic 7 decoding and record those outputs into Vegas.