Just had a quick question for you.
Did you connect the External IR Blaster on the Slingbox 500?
The Slingbox 500 does have an Internal IR but if the Slingbox is on a different shelve and the Internal IR is not in line of sight of the cable box, the Slingbox would not be able to send the signal to the cable box to change channels.
If this is the case, I would recommend connecting the External IR Blaster to the Slingbox and place the pyramid part in front of the cable box about 2 inches.
Hope this helps!!!
Sling Media Moderation Team