fuse for amps power cable

Hello guys, I bought today a 4 channel TRF M600.4AB amplifier and dont know what fuse to use for power cable. On the internet i have read that because my amp has 2 fuses 40 amps each, i have to use a 80 ampere fuse. But my amps manual says that i need to use a 40 ampere fuse. What is the right ?