Ok, the STE3RT will need to be set up on your camera as normal and synchronized with the 600 RT flashes as described in the Canon manuals.
At this point, the Cyber Commander will need to be set up with the receivers as described in our manuals (we can also provide further assistance as needed). Now, the Cyber Commander will need to be plugged in to the PC connection of your camera.
If your camera lacks a PC terminal, you will need one of these to provide a PC terminal as well as allow TTL signals to pass through. This would go into the camera's hotshoe and the STE3rt will sit in the top.
http://flashzebra.com/products/0268/index.shtml Now, there is no real recommended place to put the Cyber Commander, as it is designed to go into the hotshoe (which is occupied by the STE3rt, which also requires the hotshoe). Because of this, we do recommend the CST (
http://www.paulcbuff.com/cst.php) which is smaller and will be easier to manage connected to the camera than the CC would be. Cyber Commander would still make adjustments, but the CST would trigger.
I would also recommend avoiding mixing TTL and manual flashes. Therefore, the 600RTs should be in manual mode.