I seem to remember some VST plugins that can create a kinda 'fake ambiance', but really it is not true 5.1 surround, for that you need to have the original mulit-track recording and re-mix from scratch, for a 5.1 sound scape.
I'd say if you goggle about you may find some other free stuff that may make a sorta kinda 5.1 from a stereo source.
Remember what your trying to do is like making a true 3d colour HD movie, using only a B&W VHS tape.
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