I know this is an old post from you but I wanted to let you know my experience with this upgrade.
I did lots of research on this and found a YouTube video of the BIOS settings for this upgrade.
Watched lots of other YouTube videos on this topic.
Researched here on this ROG forum site and went ahead and purchased my Samsung 950 PRO upgrade.
Well, did everything as per the various "suggestions" - BIOS settings, remove all other HDs, removed attached USBs, etc.
Booted form a Retail Win10Home USB only to be asked at the start of the OS load for a NVMe driver.
Well, I was under the understanding that Win10 HAD the drivers.
So after messing around looking for drivers - to no avail - I decided to "think outside the box".
I re-connected my boot SATA SSD HD and CLONED it to the new M.2 SSD using the free Samsung cloning software off their site.
Disconnected the boot SATA SSD and re-set the boot order.
All is working perfectly now.
How did your upgrade go?