Just out of curiosity. If someone were doing a self ITB master how would you make everything below 100hz mono? I do most of my mastering with ozone 5 at the moment.
With Ozone you just go to the stereo spread section and set your frequency
in the upper section (where you set your frequency bands) and then grab the slider until you're all down (means zero stereo). For more precision you can also "solo" that frequency band.. You can check what happens on the correlation meter, you'll get a straight line.