Nope, that's not it either Darlak! I design AND PRINT in CMYK all the time with my XC540, they are still grainy! Color profiling has been disabled since I got the machine, no difference.
Its always a bit more grainy whenever I have K in the image, but that's because its a prominent ink. I've cleaned the heads generously with no change, changed profiles here and there with no change, even lift the heads to give a more "dispersed" pattern, just a slight difference with a bit softer look to the print.
Haven't tried slowing the print down though, I'll try that on a job today, see if that changes the "grain effect".
Chris