I've just emailed you my 5-box config - extract the files where instructed in the mail and you should see exactly what I have set up... you can then tweak it to your desire.

But to answer the question, dxNothing is part of ISBoxer - you'll see in the config when you load it into the ISBoxer toolkit that there are characters EVE-PVE-01 to 05 and a dxNothing character, which gets loaded into slot 6 and runs on the right hand monitor in my setup.

dxNothing then hosts the video feeds - you define source windows on each of the 5 clients (identical windows in this case) and then have a viewer window on the dxNothing for each source feed

If you've loaded up my config, go to one of the clients and press ctrl-shift-alt-g to toggle the GUI on and you will see all of the video feed source windows for that client - do that same on the dxNothing window and you will see the viewer windows