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You must remember that the same magnification in compound microscope vs stereo is not the same since the focal distance is different i.e. With 40x magnification in stereo the focal distance it lets say 10cm but 40x in compound has a focal distance of lets say 1cm so the image at your eye will be much larger and detailed. I don't think there is a replacement for compound when looking at very small objects.
Also from my experience if the current magnification of the stereo microscope is not enough it'll probably will be a little better after another x2 but still too small.