Proper installation and configuration
I have just purchased the SG-1000 and am unable to get it to work. I've installed it between my BT provided ADSL modem and my Apple Extreme wifi router. The SG-1000 works when I directly connect my computer, however it doesn't work when I attach the wifi router. Is there a configuration change that I need to make on either the Extreme or the SG-1000?
You probably need to setup your Apple router as an AP.
Probably they are both using the same internal subnet, 192.168.1.0/24, which is causing a conflict on the Airport as it tries to route/NAT between them.
If you change the pfSense LAN subnet to something else that will probably allow it to function but switching the airport to run as an access point only is the better solution.