I'm using a GTX 1080 on this machine, have the latest drivers, and the CUDA development kit, but I still can't change the Compute Device. In fact, I can't even see the selection "None". The button doesn't show up at all.
the screenshot for my user preferences.
Specs:
i7-6700K
GTX 1080
120GB SanDisk SSD
Windows 10 64-bit