New to xeikon CX300, imposing..

Hi!
I'm learning about this new CX300 (and X800 sw), but I can't understand how to do the imposition via an external software, what is normally used?
There'are any ad hoc imposing sw? I have many different old DIE in stock that I should reuse, and I don't want to make a mistake - thanks and sorry for the many questions, I'm new.
(ps.: internal layout step & repeat isnt so precise and I want a 2,235mm interspace between each singole pose)..