Shadow: Existing RGB cable?  It doesn\'t come with an RGB cable.  It comes with 3 rca cables, but one is video and 2 are audio.  Your adapter would require you to have an RGB cable for that to work.  It wouldn\'t be any better than just getting the S-Video cables to begin with.
AK:  S-Video is just video, hence the name.  You still need to use the two rca cables or buy optical cable for audio.
Phoenix:  Monster is a brand name of regular old cables.  They are a little bit better than normal ones, but much more expensive.  They make S-Video cables, RGB, etc...