I have the same router as you.
and I initially set it up via the port forwarding (gaming port)
Unfortunately, unless you have a static IP (most people don't) you will have to constantly reset your ACIII everytime there is an IP change. Obviously this defeats the purpose when you are away from home.
A friend of mine set me up with TZO.com and configured the settings via the DDNS under basic setup tab.
Sorry, I don't know much more about it since I'm nearly computer illiterate, but I can at least share notes with you and tell you what settings are set to what on my linksys, just from observing the routers management page. I guess you have only two choices: TZO.com or DynDNS.org
Either service will manage your changing IP for you...unfortunately it is a sign up service. I'm still under the 30 day free trial, but from what I saw, I think it is nearly $100 a year for the service - $35 for the domain name (yes, you get to choose) and another $59 for the maintenance service if I remember correctly.
Then you simply type in your domain name from any browser to access your ACIII (from anywhere)
Once this is done, then you can configure aquanotes (if you have it) to access the controller without needing the serial cable to interface the two.