A Normal Question... How can I extend my coverage of WiFi etc...
You can use another router to use as a Bridge or Repeater...
A (Wireless) Router is basically a Switch, Hub, WiFi Access Point (AP) in a box and it can do marvels.
Connection will look like this
ONT-----Main Router (ASUS) ========(RJ45)====Second Router========Third Router
As there is 4 LAN PORTS on the ASUS Router (N15, N56, N66) , you can use either a STAR Configuration or a BUS Config, depending on the way you route it. Does NOT MATTER
LAN Port 1 of MAIN Router goes to LAN 1 of Router 2 and LAN 4 of Router 2 goes to Router 3 LAN 1 in a Bus but in Star it's 1 ++ 4
You need to DISABLE THE DHCP ON ALL ROUTER EXCEPT THE MAIN connected to the ONT.
You need to Assign an IP Address that is the same subnet on the network, usually 192.168.1.252/251/250/249 and so forth.
You need to set a DIFFERENT FREQUENCY BAND and SSID to differentiate the routers (say Main is MYREPUBLIC and second is MYREPUBLIC-2 etc)
The above is how you set the frequency for N56U which is UPGRADED.
However, if you are using an old Singtel PACE 5520 or NV5012, you can also use it to do so.. but do note of the Fast Ethernet port (100mbps)
DO NOT USE A HOME PLUG