Thanks for the feedback Alan. I just checked and do see that there are gamut warning issues on this image. But I'm confused by the plain paper situation - why would plain copier paper at 360 dpi look so much more right? I used the same ICC profile for it.
I don't think you can apply an ICC profile to a paper that it has not been created for as the results will be unpredictable. Plain paper is also not coated in the same way photo inkjet paper is and the dot pattern is likely to be quite diffuse as the absorbency is different (you can check this by looking with a magnifying glass).