On the diagram. although it shows a third wire from the display side for the rheostat, only 2 are shown entering the Head unit from the brown connector - so probably the third wire is not needed as the rheostat lighting is particular to the Colour display and can be set independently.
- As for fitting. Again - make a copy or printout of all settings in the BSI first for the old unit in case you need to revert back temporarily.
- Before fitting any of the new units, use Diagbox to ensure you have the right configuration for screen and head unit and VIN code the unit (unless they have done this for you beforehand). Once configured, I would do a BSI reset to reboot the systems and then see if it all works.