Here's one method that is sure-fire.

1. Set up Maxis router as per usual, and then DISABLE wireless.

2. Set up any other router as per usual (you want the router to act as if it was connected to a device that served direct access to the Internet, which the Maxis router is doing. ASUS routers call this setting "Automatic IP". You must not attempt to connect via PPPoE or any other method that requires username/password).

3. Set the Maxis router to DMZ your custom router.

That's it. Remember to reboot your custom router once every 48 hours or so.

Somebody's said that if you turned your Maxis router into a bridge and used the (ASUS, in this case) custom router to log in via PPPoE, you can even put the ASTRO on the custom router, and you don't have to reboot the router every 48 hours. I haven't tried that; maybe I will one of these days and see what happens.