Just used this with my Win 8.1 x64 VM with the following USB devices:
Logitech MX518 mouse
HP USB Keyboard
Microsoft Xbox 360 Wireless Controller
FLIRC USB
Previously using the GUI, the system would only recognize the KB + M, and there would be a device with no properties called "vport0xxx" (x = forgot, sorry).
Using the above xml, the system immediately recognized all USB devices, all in <1 minute.
Additional to above, I had to go from:
<controller type='usb' index='0' model='ich9-ehci1'>
<address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x7'/>
</controller>
<controller type='usb' index='0' model='ich9-uhci1'>
<master startport='0'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0' multifunction='on'/>
</controller>
to
<controller type='usb' index='0' model='nec-xhci'>
</controller>
Hope this helps!