Asterisk 1.8 and FreePBX 2.9 and Free Fax for Asterisk

I am trying to get Free Fax for Asterisk working on my asterisk 1.8+freepbx 2.9 system. I installed the Digium Fax module successfully with the free license. When I try to enable fax detection in FreePBX I only get DAHDI and SIP as options, NVFAX is greyed out.

How do I enable fax detection on my inbound IAX trunk?