I'm not sure I understand the problem correctly.
The connects 2 devices allow the head unit to be controlled by the stork, other connects 2 boxes allow the reversing sensors to work etc. The ISO connector allows the Peugeot built in multi connector behind the dashboard to fit to a different head unit, so its specific to Peugeot and the head unit (which is usually a standard fitting - but not always).
As far as I'm aware no aftermarket head unit functions will show up on the orange/black display on top of the dash - Connects2 stated that on the tech pages of their website.
The "flipping" between mph and kph would seem to indicate a problem with the stork control, as that is how you would change the standard display configuration.
Not sure that any of this helps, but as 2Retro says, many of us have changed the head unit and managed to get all working.