The Sum row of modules is used to mix the output of two or more Rooms of the same output configuration and in some contexts, to sum inputs directly without the use of Room.
The Sum module can handle different input configurations. It will Sum channels based on there channel names, so correct naming convention is important. Summing a 5.1 and 7.1 room together will output a 7.1 where their common L, C, R, Left and Right Surround rear channels will have content summed from both rooms the but Left and Right Back surround will be only from the 7.1 room.
★ Summing can also be done directly in Output Modules
The Master Transcoder row of modules offers an opportunity to consolidate the various formats you might have been mixing into one (or more) formats for final output routing by the Output modules. The same options and routing are available as in the Input Transcoder modules.
Finally, the two bottom rows in the Envrionment Setup graph are the output modules for the entire project. The Binaural Monitoring row provides a way to decode the whole scene to headphones only in binaural 3D (see section 5.1).