There are so many variations of this machine globally its hard to keep up.
Reading into your post it sounds like you have a spinner in bay 2 and a 128 M2 SSD in bay one. Is this correct?
ASUS played a cruel joke on this machine. Bay 2 is SATA II, not SATA III. Putting a 850 EVO there is a waste of money as it will not see that 500MB/s speeds. The other side where the M2 slot is also has a SATA connector that is SATA III.
Samsung magician provides no advantage nor do Samsung drivers.
Your best bet would be to replace the existing 128MB drive with a larger M2 PCIe AHCI drive like this one.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820147425Next choice you can put the 850 evo in the SATA III port but will either have to do some modifications or remove the 128GB M2 drive for it to fit.
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein