Thanks a lot for your answers. Howerver, still, nothing's working.
nudone> thanks for taking the time to do these tests. I tested Dopus and it didn't display the image correctly. I don't have Adobe Bridge so i can't test it.
philB66> nope, LilyView doesn't do the job either.
Here is an image that can be used to make some tests : cmyk_test.jpg (93.65 kB. 406x377 - viewed 658 times.)
(edit : i changed the post so now there's a direct link to the image)
And here's the difference between real colors and false ones :