Add new source button (the "plus" icon in the middle).
When we click the Add New Source button we can select the input type from the context menu:
Add new source menu
Once we add the new source it will appear as a thumbnail in the Input Strip:
2 active input sources
Now if we want to use the new source in any particular scope, simply right click the scope view and go to Input Device to expand the list of available input sources:
Select the active input for a given scope
Input sources are color coded, when the thumbnail in the Input is highlighted it shows a frame around all the scopes that are assigned to that input source.