Many apologies for late reply.

* OSX Firewall settings for Tiger IF it is turned on, though you say it is turned off.

* I cannot figure out if your AVR-8000 is a modem or router. Try connecting directly using the AVR-8000. If still no good, try connecting directly using your AirXpress. Also see Apple Airport Extreme/Express for Mac users * (NAT-PMP)
If you do need to port forward the Airport then first & most important step is Setting up static ip for OSX & choose port 64049 or 4915. Then use same port here Manual port forward instructions & sample image

* Also see (a) If LW Will Not Connect, __ (b) Problems with the search, __ (c) Hostiles List

* Under LW's settings, preferences > Advanced > Firewalls, change both connection & listening ports to the same above such as 4915 or 64049.