Accessing system settings

I'm a new 2004 Cayenne turbo owner. The vehicle is in excellent shape, but it has an aftermarket head unit which is ok. I've been running through the owner's manual and it seems like a lot of the vehicle's system settings are accessed through the factory head unit which the current unit can't access.

Question: Do I need a factory head unit to access these settings? I'm concerned that there could be warning messages that the system might produce that I won't be able to see if I don't have the factory head unit. Are there other things I should be concerned about if I don't have the factory head unit?

TIA.