Airfoil Source for "Speaking"

To get the "Speak" text to broadcast through the house via iHome speakers, what do I set the 'source' to System Audio or do I select other application - Indigo 6?

Any specific settings in the Airfoil plugin I need to check?

You can run it though system audio (keep in mind you would have to pause anything else running so BOTH audio sources don't broadcast) or you can do what I do and switch the source to IndigoServer.