Thank you for posting your question to the answers forum! That's a great question. Unfortunately, the HD connected cable for the Slingbox PRO will not work with the Slingbox PRO-HD. The reason is because the HD Connect cable for the Slingbox PRO plugs into an HDMI port, which the Slingbox PRO -HD does not have. Therefore, it will not allow you to connect that HD connect cable. I do apologize if this is any inconvenience to you.
Hope this helps!
The Sling Moderation Team