The Velocity Solo x2 with a Samsung 850 Evo 1TB SSD was installed in PCIe slot #2 right next to the Nvidia card. The SSD came from my MacBook Pro and already had Yosemite 10.10.5 but I reformat and cloned the Mac Pro hard drive to it using Disk Utility Restore. When the cloning was done the Mac Pro was able to boot from the SSD with no problem. I enabled TRIM on the SSD an restarted the Mac Pro two more times to make sure everything was ok but I made a few post-install observations: The About This Mac Storage tab reports the SSD as external. Disk Utility Get Info reports the SSD as ejectable and Disk Utility sidebar shows the SSD as an external drive with the orange ejectable icon.