Thanks for using our forums here, that's a great question! I understand that you are interested in viewing the Slingbox 500 on 4 WDTV players simultaneosly. However, you can only stream to one device at a time with any Slingbox as they are not standalone cable boxes. The "Remote viewing on 4 screens" feature is referring to the potential of viewing on different types of screens, ie: mobile devices, tablets, remote TV's and PC's or MAC's. I do apologize about any confusion and/ or inconvenience.
Hope this answers your inquiry!
The Sling Moderation Team