You changed the red and white audio cables?
I know you already connected to a different cable box, and got the same issue. I would try to confirm if the issue is with the Slingbox itself, by connecting it to a DVD player or something similar that uses the same source you are streaming from. You wouldn't have to reset the Slingbox or reconfigure, if you are just going to stream from that other device the Slingbox is connected to. This might help narrow down the issue.