These are cables that are able to convert the Mega Drive's a/v out signal into pure analogue RGB, or convert the RGB to s-video, so that you can get the best possible image from your Mega Drive. Does anybody have any expierience with these? Is so what are ups and downs of these cables? Also, does anybody know where to get one? Here is linky describing the cable.
http://www.segagagadomain.com/hardware-mega/xmd-3.htm