I looked on the support page and I don't see a QVL. That's not uncommon for laptops since they nearly always come with compatible memory installed. No QVL means ASUS probably didn't validate more than the few kits that came pre-installed.
It comes with 3200 memory so I wouldn't expect it to run any faster. If you buy a 3400 or 3600 kit it will probably only run at 3200 anyway. So just buy a 3200 kit in the capacity you want and make sure to buy it from a retailer with free returns in case you need to exchange it for a different brand.