sunk818, if you look at the chart, it shows that you should only need 1.32V to run at 200mhz.  If you have them at 1.5V you are pulling around 1.82A.  Can you check the specs on the pluggable hub?  The one I saw mentioned a limit of 1.5A/port. 

Is this what you have?

http://plugable.com/products/usb3-hub7bc/
"USB over-current protection supporting up to 900mA per port (up to 1.5A for BC 1.2 devices)"

It's possible that the hub is shutting down the power at some point. Unless you are planning on running at 300mhz, i would drop the vcore way down.