You'll get a lot of answers on this one. Calorie burn depends on a number of factors: for example your weight, your overall fitness level, how much sleep you got the night before - well, you get the picture. The last time I did IMAX2 I burned 266 calories (on an 8 inch step and no modifications). Like others have mentioned, I also get a better burn from a steady state cardio than with any of the IMAXes.
You should get a heart rate monitor. It's been one of the best fitness investments I've made besides my Cathe videos of course!