There are usually 3 PT stations on a dub stage. One for the fx editor, one for the dialog editor, and one for the music editor. The mixers often also have monitors/mouse set up on some sort of kvm switch so they can look, take control of any of the three systems while they are mixing. The stems are then usually routed to a recorder and/or additional PT rig in the machine room and recorded all at once.
This system is efficient and works well when every station has a talented person behind it :)
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