> On the host I see this USB3 device. It seems it doesn't support Passthrough. I assume it means it will not be possible to see this from the VMs.
user9922, you appear to be confusing PCI passthrough and USB passthrough. You are correct that passthrough of a USB 3.0 host controller as a PCI device is not supported. This is true for any host controller or hub. USB end devices can be passed through. In your case all of your USB devices appear to be attached to USB 2.0 ports. To passthrough a specific USB 3.0 device other than a hub or host controller please try the following:
1) Add a virtual USB 3.0 host controller to your VM. This is a virtual device just like the USB 1.1 and 2.0 host controllers that you already have.
2) Ensure that the USB 3.0 device is attached to a USB 3.0 port (i.e., a blue one)
From your original lsusb output the USB drivers are reporting that all devices are on a physical USB 2.0 bus. The "root hub" is in fact the host controller.
[root@localhost:~] lsusb
Bus 001 Device 004: ID 045e:0752 Microsoft Corp. Wired Keyboard 400 <<<<< Device on bus 001
Bus 001 Device 003: ID 0557:2008 ATEN International Co., Ltd UC-232A Serial Port [pl2303] <<<<< Device on bus 001
Bus 001 Device 002: ID 0781:5567 SanDisk Corp. Cruzer Blade <<<<< Device on bus 001
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub <<<<< Bus 002 is 3.0
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub <<<<< Bus 001 is 2.0
[root@localhost:~] /etc/init.d/usbarbitrator status
usbarbitrator is running