Why is my Oki printer printing multiple copies one job at a time?

Our office recently installed a new Oki CX2633. It's a great printer/copier. My problem is when I want to print multiple copies of a file. It appears that the printer is doing each copy one job at a time. It will print one, and then load new data, then print another, then load new data... Printing 20 copies of a large graphic file (ie. a poster at 60-70 MB) can take up to an hour with 2-3 minutes between each copy.

I've installed the driver from Oki, which doesn't work great on Snow Leopard (struggles with 64 bit), but it works. I've tried printing from Photoshop CS4, Indesign CS4, and Apple Preview (prints faster, but still same problem).

Any Ideas? Thanks in advance for reading and your response.