There are many different models of 1084 monitor. Some have a DB9 input, some have a round DIN. Your best connection is going to be from the Amiga 23-pin output to the correct input on the 1084 (i.e., don't use the composite ports or anything like that). If you post a pic of the back of the 1084 someone should be able to send you a link to the correct cable to buy. Good luck!
http://gona.mactar.hu/Commodore/monitor/Commodore_monitors_by_model_number.html
