I've experienced similar trouble. Converting the RGB image from Poser to printable CMYK, I find that the histograms of each channel has bad ranges. If you know what I mean. E g., the green channel runs from 1, but not to 255 - it makes an steep peak and then an abrupt halt at around 160. The blue and red channels are the same, on other levels of the scale. So, color mode conversion don't help - the scale in each color channel doesn't spread over the whole range. There seems to be some shortcomings in the rendering. ... or maybe I used bad lighting. :)