Just to make sure it's clear, a regular "oppass#" user login (which you use the "login" command for) is what's used for the "remote admin" menu. Your password for "login" is what you'd use here.
Rcon is for true remote administration. I don't know of any fancy ways to interface it currently. To do it in-game (you don't need to be connected to the server), use:
rcon_address=myserver
rcon_password=mypass
rcon say hello people, how are you
