Monitor output or Main Analog Output?

Hey,



I have in my studio:

- 003Rack

- headphone amp

- powered monitor speakers



I need the output signal to be assigned to my monitor and headphone amp. currently, the headphone amp is connected to the 003Rack in the main analog output 3-4 and I'm connecting the monitor to the main monitor output in my 003 rack as well. However, while surfing the net, everybody was saying "connect the monitor to the main analog output 1-2".



Why do I have to do that? and if so, how will I be able to control the monitors' gain?