like you I don't see a difference on screen, but I may not be doing it right, it's a long time since I bothered with cmyk in xara - there is a difference though when exported as PDF/x

so I think that it may be it does not show on the screen as some of the info from xara imlplies, unless as I say, we are doing it wrong

as you are using pro+ you could go to the xara website log on and ask the question via chat referring them to your posts here; be interested to know what they say