That's really good news.
I think I've found the problem. Damn! Why is it always the simplest or littlest things?
I went back into my Sling's menu to Connect-->Video Input and noticed that S-video and everything EXCEPT composite was grayed out, meaning that only composite was configured. So I switched the connections to match that and voila! It works.
Now I just have to figure out how to configure S-video and I should be able to utilize that feed. Can you refresh my memory a bit on that?
All the HR21 outputs are turned on concurrently, so you're set on that side.
"Configuration" is really done through the Slingbox software setup wizard....its pretty "automatic. Either go in the Setup Assistant dropdown in the Setting menu on the software menu on your PC, or else, use the install CD to run the setup.
Now we're anxious to hear if you get it up working...