there is always something you can do

thing with router is they need tobe setup aswell. check in your amule-preferences under connections what ports are set for tcp and upd (standart is 4662 - tcp and 4672 - udp)
now open the admin console on your router and look for something like
--nat
--virtuell server
--port forwarding
there are many words for the same thing so I dont know how its called in your router. maybe you should check the router manual on howto forward ports from the router to maschines inside the lan.
only thing you need todo is the forward the ports in your amule prefs to the IP-Address of your mac-box.
its not really hard, there are often examples in the router-manuals.
They usually explain it with http-servers(apache), just take this example and change from port 80 to 4662/tcp and 4672/upd.
hope that helps