I have looked everywhere for where exactly it states you need a "magical" enhancement but I just haven't been able to find it.
It merely states that you need an enhancement bonus, and adamantine gives you one when you make armor out of it.
You can consider the armor to be masterwork and to have an enhancement bonus of +1, +2, or +3 for light, medium, and heavy armors, respectively. The masterwork quality does NOT reduce a armor check penalty.
If you can show me where it says you need a "magical" enhancement to add special abilities, I'd like to know where, as far as I've seen all you need is any type of enhancement bonus.
Aluvial