Fork with 6" Post Mounts (some forks have 7" Post Mounts and you can't use a 6" rotor) + Post Mount brake + 6" rotor = no adapter needed, the brake will bolt straight onto the fork.
Photo of a PM fork with a PM brake.
Photo of a IS fork with a PM brake & adapter.
The fork in question has the 6" Post mounts.
http://www.marzocchi.com/template/de...dOggetto=56816