You need bridged mode. If you don't it will always cause you headaches.
If it's feeding receivers for some form of IPTV he might not be able to put it into full bridged mode unless he's got a specialised third party router that'll do VLAN. I know that's the case for the Bell FibeOp setup, and suspect his is similar.I'll check as for disabling they prob can't as it used to give other 2 receivers signal.
you beat me to it clshadesCan you clone your Asus router to the isp router? Or maybe you can use the Asus router as a access point instead? Then you get all the benefits of the Asus router speed wise and the isp router controls the dhcp.