Can't open xbox live NAT on Zyxel PK5000Z

My friend has Qwest for an isp, and they gave him a Zyxel PK5000Z modem/router combo. His xbox is connected via a Belkin wireless router thats configured as an access point (and the access point is working fine; connecting straight to the router didnt help). I've tried the following, but nothing can get rid of the strict NAT...

Turn on upnp -when I restart the xbox, the upnp status page doesn't show the proper ports as being opened by the xbox

Static local IP + port forwarding - all the ports are forwarded, restarted router and xbox, but no luck

Static local IP + DMZ - set the xbox as DMZ host, but still no luck...

I'm out of ideas now... anyone have anything else I could try?

wow i cant believe DMZ didn't work that always works with xbox's,im guessing its just the modem/router combo they gave him im assuming its not xbox complaint alot of routers can be fussy with xbox and the port forwarding of UDP 88, UDP 3074, and TCP 3074. no clue why but ive never hear of dmz not working on the xbox.on the old 360 dashboard i had to do a network reset in the system tab a few times from getting a half open connection.but im sure you've tried that.only suggestion i have would be for him to buy his own equipment i hate to use what the isp's send me.

I've tried rebooting xbox and router multiple times and nothing seems to work :/ even re-doing the connection in the dashboard a few times.

Stupid Xbox man... This issue is now SO common and so complained about that they made a Major Nelson 'help' video accessible from your 360 dashboard explaining how to work around it. Guess what? It lacks depth and does not work on all router models! No way!

here is a list of compatible hardware for live..http://support.xbox.com/en-us/pages...ng/network-hardware-compatible-xbox-live.aspx