Dear adamcarney83,
it is well known that the CMYW is printing darker than usual CMYK printers. Normally marrying with B should make the colors better. If you are still not happy with the result you have two options.
Upgrade to the latest RIP version with the best possible color reproduction and use the latest RIP profiles from this website or increase the fill up value from 150% to 200% or even a bit more.
BR
