You should just be able to go into the settings for the room that has the PLAYBASE in it, and click on "Add Surround Speakers".
To clarify, when it asks if you see the green light, just say yes (your speaker is already part of your system and doesn't need to be paired). Then when it says to press the two buttons, press them on the existing speaker that you want to add as a surround. Not exactly intuitive, but works...
