Thanks A Fairley, I downloaded and printed your test image, but unfortunately there's the same yellow/green cast.
I've doubled checked everything (including nozzle checks and flushes...all the magenta inks are operating fine), but the problem persists.
I'm beginning to think it's an issue with the Eizo CG277 monitor and Mac Yosemite. My previous computer died and I replaced it with a new Mac Pro which had Yosemite already installed. Eizo advised against upgrading to Yosemite as there's a problem with this OS and their built in calibration system. However because it's a new computer I don't have a choice but to run Yosemite. Eizo advised that calibrating with a third party device (I'm using a ColorMunki) should work, but I'm coming to the conclusion that there's still a problem.
In the meantime I've got a clunky and not particularly accurate soft proofing workaround, and I guess I'll have to persevere until the Eizo/Mac fix arrives. Black marks to Eizo/Mac for allowing this to persist long after NEC/Mac have sorted it all out!