"Add second ssd to new mac pro... Possible?"に関する回答Anandtech looked at the PCIe map <http://www.anandtech.com/show/7603/mac-pro-review-late-2013/8> and found the most likely arrangement to allow only a single SSD controller. There must be a difference in the mega connector pinout between the two cards to route the PCIe lanes to one side only. But don't let that stop you from trying it out and reporting back if it worked or not!