The only reason to use Virtual 5.1 is to generate 5.1 channels of output from a stereo source.
It's very simple: the rear outputs are copies of the front, the center is a combined copy of the front L/R and the subwoofer is a combined copy of the fiver other channels.
Virtual = not real = fake = crap
If you have PowerDVD or WinDVD you can decode DD to 4 channels.