I have heard the Master Tracks and Monitors. I was hoping to be able to get my hands on the new XC model, but no such luck it seems :/ I can tell you that the Monitor are definitely ahead of the Master Tracks. Can't comment on the XC model unfortunately. It's been stated that the XC model is supposed to be an over ear version of the Tracks Ultra, but I can't confirm this. If that statement is true, then I'd definitely place the XC model ahead of the Monitor. Unfortunately, I can't confirm it, so it's still taking a chance.
Neither brand is really that popular on Head-Fi, so I'm not sure if you'll get a lot of hits here from users that have both models.