I got the pulse-eight adaptor working by adding the address manually to the xml for the VM.
<hostdev mode='subsystem' type='usb' managed='yes'>
<source>
<vendor id='0x2548'/>
<product id='0x1002'/>
<address bus='7' device='5'/>
</source>
<alias name='hostdev1'/>
</hostdev>
The above is the code specific to my installation but it might be of some use.