Thanks for the reply and help @kiiroaka !
I think its a strange problem, when i dual boot it to my windows 10, the usb 3.0 works just fine on the front headers and everything works well. Its just in sierra that it starts acting up.
Im facing the same difficulty, with no USB 3.0 drives being recognised on the front panel.
My specs are
MSI Z170 Sli plus (2 USB 2.0, 2 USB3.0 rear, 2 USB 3.0 Front)
2 x 4gb Avexir 2400 ram
Asus GeForce 980 Strix OC
imac 14,2 system definiton
Phanteks Evolv ATX TG case...