This is a difficult question to answer without seeing the picture as I would never convert into CYMK before making a PDF. Minimiro is right as Xara will reconvert the photo back into RGB which might give the photo a real washed out look, you'll discover quickly that each 4-color process behaves differently when the ink meets paper. And only experience will serve you in perfecting your process. Presses are like people and cars; each behaves a little differently.

What I am really trying to say if the photo is not the main part of the drawing it might be fine as you can bring up the levels using the Photo Tool. If it is a picture of a person then the skin might be an odd colour and really the use of PS is a must. There is real skill required to get the gamut right, not just using the warnings or using lab. Work with a local printing shop and get a wet print and you can find out other details which will help you. If you need more help please come back and I will try and help as well.