Hi, I am on a cMP 5,1: 12x3.33/64gb/GTX 980ti 6gb running OSX 10.12.6 If I choose startup disk to Win7, I boot to Win7. However I get stuck there and cannot get back into OSX. Choosing startup disk from Win7 does not work, neither does the restart in OSX option. My OSX drive disappears and cannot be seen (which was the case previously) from Win7. Obviously I have no boot screen. I will either get a No bootable device text message, or just a reboot into Win7 from Win7. It literally takes me to rip out the GPU, replace with EFI 680, remove OSX hdd and reseat in different SATA slot, remove Win7 hdd and hold OPTION to see the OSX drive. So clearly this is a really odd issue. I had no problems with earlier versions of Sierra with startup disk boot selection. Any insight and ideas would be greatly appreciated. Thanks for the time and consideration!