Check the total ink % in the info box. If the black is lower than 260% (if your going sheet fed) then use curves to boost it up. If it's between 260% and 280% then your print will be fine. And Check the yellow level in the black mix. if it's too high then the black will look dull. if they are all fine then the dullness is a limitation of the proof printer Extra note: make sure you don't embed a profile. it's better to leave it untagged (saved w/o a profile) since you have no clue what the printer might convert the colour to.