The easiest thing to do would be to have 2 TV graphics side by side that represent the 2 displays. They should be big enough so that you can have 4 buttons inside of them.
Inside of each TV have the 4 source buttons. These buttons launch macros that send that specific source to that specific TV.
The only thing staff has to do is press the source button for the TV they want it on.
You mentioned speakers but not how many pairs/zones/whether or not you will have the ability to hear different sources at once etc. If you only have 1 pair of speakers i would do another graphic of a book shelf speaker with the 4 source buttons over it. That way they choose video for each display then choose audio for the speakers.
I tried to post a screenshot but my hosting account isn't letting me access via FTP. Might be the network im on right now. I will try and post later.
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