ac-3 pro plugin and dolby surround

[ecc]

I'm playing around with a friend's laptop that has Sony Vegas and the AC-3 pro plugin and was wondering how to create Dolby 2.0 Surround. I'm assuming that if I had a 5.1 project and I decided to render it as 2.0 LR with "Dolby Surround Encoded" selected then it would know where the surround channel was by the 5.1 panning but if I wanted to upmix a stereo track to surround, would I have to invert the phase of the created surround channel (V.I. VST on a stereo track and combined to mono at -3 dB) myself or would the plugin do it or does the phase have to be inverted for the plugin to know which one is surround?

As I say, I'm just playing around. The 2.0 surround test that I put out from this file sounds much the same as the original stereo track does with PowerDVD's Cyberlink Headphone or one of the other 3D virtual sound plugins so a Dolby receiver would have good results upmixing but I'm still curious. I find the matrixing process interesting.

[aedipuss]

with vegas going from a stereo source to 5.1, all it does is copy the front channels to the rear. your choice in the options to invert or not and the amount of change in sound level.

stereo to 2.0 doesn't change anything. it's the amp or software that decodes the 2.0 into r/c/l with the sound that is the same on the left and right channels going to the center.