Yep bluebubblea, the 2nd bay is only SATA II, and then there is the issue with sound. I would have worked around the sound issue since we've had it since the G75VW, There are a couple of different mod out there one to re route the SATA III connector in bay 1 then you could have the m.2 drive and SATA III drive in bay 2. Another one I've heard of is taking well with your model you won't have the M.2 adapter anyway but to mount the m.2 with tape and then a SSD without the caddy would fit also being taped in place. Yep I have a JY in my cart at xtopic and finding this out stopped me from checking out. I have no Idea what Asus was thinking to put a SATA II connection in the 2 drive bay.
One thing though the M.2 drive would be much faster than 2 SSD on SATA III connections in raid configuration. These current M.2 SSD are really fast and with new generations coming out soon I wouldn't get to hung up on setting up a raid.