I think, I'll try to find some empty hdd to fiddle with this. But if the case is about firmware's ability to handle 8TB hdd's through usb, I can't test that. I don't have any spare 8TB's luying on the shelf..."With usb, it just invokes "Initialize..." window."
Have you tried going further?
That is... have you tried to use disk utility to erase a drive and see if that brings the USB connection "alive"?