I work for newspaper & printing company in Scotland do book covers and adverts for weekly colour supplements so take work home to finish and start. Never have huge problems opening and closing docs. unless it has effects not supported by the other programme and bitmaps especially tiffs and also Xara always converts CMYK bitmaps into RGB bitmaps on importing and that is why I think you are getting the colour shifts even with simulate printer colours turned on. I use either Illy or even better InDesign to assemble CMYK bitmaps and vectors together and then you can do the preflight in one go and be as confident as you can be when taking files down to the print room.