It is not currently available to specify directly as a source.
You could make a CC that will put the Scene on the PST for you and use that instead of a direct call to the source.
Or you could use an Aux bus (they don't have to actually be assigned to an output..) as a virtual bus. Then you use that as the source that you call. then what ever you assign to that aux would be put on PST for you.
Only useful if you might want to call the Scene to multiple places and don't want to have to build a few CCs for each Scene and Crosspoint.
Just call Aux 21 - 24 then have a memory of CC that puts Scene 1- 4 on those auxes during the show setup file or part of the RSTATE.
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Les O'Reilly
Director - Switcher Product Management
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