We have a whole bunch of 4102's running on the voice network.
On the 3300 ICP I have them set up as Generic SIP devices.
The SIP configuration on the Mediatrix has the following fields as the controllers IP address:
Registrar Host, Proxy Host, Outbound Proxy Host.
Make sure the SIP User configuration field has been completed with the correct DN.
When on the network you can see the attempts to authenticate against the 3300 in its Software Logs, you can trouble shoot any issues from there.
One thing I did find is that if your using relatively new FAX machines with these SIP converters you will need to disable T.38 codec to push fax through G.711.
Hope this helps