Hi I have tried to do that by disabling dhcp, nat and firewall on the brightbox but still does not want to work.
I read the Apple Airport Extreme has no firewall, I don�t like that.
Try this, disable the brightbox wireless, then configure the airport extreme as wireless access point. Disable airport extreme router WAN and DHCP and connect with Ethernet cable to brightbox LAN port from airport extreme LAN port and it should work.
You should be able to use the Airport Extreme other 3 LAN ports and the wireless connection and if you wish you can also use the brightbox wireless connection.