I know nothing about that machine or controller but honestly I'd upgrade to some sort of PC based control that would completely do away with your memory issue. Basically you have a 20 year old controller there. You could shop around and find out what options where originally available for the machine, but being a 20 year old machine I doubt they had a memory option big enough for your needs.
By the way this is likely to be a non trivial upgrade if you go the PC based control route. It might make sense to contract the upgrade out.