USB 3.0

I have an optiplex 980 with ESXi 5.5 installed. I have setup open media vault as a vm and everything was working great. I decided to add more storage using usb. I added a USB 3.0 PCI express card and enabled passthrough in esxi. the card was recognized and enabled successfully in esxi. However, open media vault does not recognize the two usb devices that I have plugged into the usb 3.0 card. I can plug them into the existing 2.0 ports on the 980 and it does work, but at 2.0 speeds. Don't know what I am missing. Anyone else had this issue before???