It seems that you are having some issues in order to stream the audio signal from your Slingbox. You will need to connect the red and white cables since the S-Video cable stream the video signal only.
In this case, you will need to connect the Composite and the S-Video cables from the DVR's outputs into the Slingbox inputs. This way, you will be able to stream out the audio and video signal.
The following link will provide you with some information that might help you.