Thanks for using the forums. You have a great question about the PRO-HD versus the 500.
There are a few differences between the 500 and PRO-HD. The 500 can use HDMI connections as well as the component and composite and also can be connected to the router via wifi instead of just the hardwired connection. The 500 also has a feature that allows you to be able to view pictures and home movies from a remote location. The articles listed below should give you some further information.
- Slingbox 500 Tech Specs
Hope this helps,
The Sling Moderation Team