Good Afternoon,
I have setup PolyCom units behind SME boxes before but they were the networkable kind. I don't believe that you will be able to setup units that are attached via USB. I was successuful in port forwarding the necessary ports for the network versions.
If it is a software package of some kind that you use to interface with the USB device, determine what ports it is attempting to talk on and open those up. There are three or four with the network versions which cover both TCP and UDP. I don't remember the port numbers as it has been quite awhile since the units were used. I hope this helps.