Hello Walshie,
i also have an MT, but i have a workshop manual. This says a new filling with converter is 9.5 litres and the change quantity is only 3.5 litres.
So if you want to chenge the complete AT fluid i would recommend to do it with a special system that is able to change the complete fluid in the system. There are different systems out there. For example a german system made by Tim Eckart that also uses a cleaner to clean the complete system and then flushes it. More infos:
Englisch
Regards, Markus