Hold the OK button for 3 seconds, this will reveal of bunch of different options at the bottom of the screen. Scroll over to the right and click on "Multiview".
Press OK again and then choose "Add screen", then choose the channel you want to add. You can add up to 4 screens by following the same process.
Note - each screen will use a connection, it will still work to add screens, but it will buffer so bad they will be unwatchable.
