Re: NEC/Renesas USB3 Controller - VMDirectpath M4A89TD Pro/U
It is my understanding that, the way USB works, each physical port is sort of multiplexed to multiple logical controllers. In other words, when you plug a device into a port, if it's a full-speed device, it gets a UHCI controller bus; if it's a high-speed device, it gets an EHCI controller bus, and a 3.0 device gets the XHCI controller bus.
Here's a website that puts it all together:http://tech.hj60.com/
So, the USB 3.0 passed through port will only work with a USB 3.0 device. If you want to use a slower device, then you have to also pass through the UHCI or EHCI controllers (and in doing so, you'll end up taking many of your physical USB ports with you).