I use Thinstation with spice-gtk 0.27 to connect to foss-cloud VM (windows 7 /8). Its works with usb and sound finly.
The Problem is the quality by Video (flash and offline videos).
Now i testet with newer spice-gtk 0.28 /0.29, but the sound is not working with the vm.
A other way for better quality is virt-viewer 2.0. with spice-gtk and spice-protocoll but i found no Pkgfile tu compile it.