i have had mixed results when reading the ASUS specifications in my past, sometimes going from international (.com) too the dutch site (.com/NL/)
there are differences... ive checked both:
https://www.asus.com/Motherboards/Z170-P/specifications/
and
http://www.asus.com/nl/Motherboards/Z170-P/specifications/
and (dutch website for price checking and reviews)
https://tweakers.net/pricewatch/457433/asus-z170-p/specificaties/
its conclusive that it only supports (quite oddly) AMD Quad-GPU CrossFireX™ Technology...