Active noise cancelling headphones should not be a problem- they work by analyzing the outside noise (they have little microphones on the outside of the earpieces)and then adding the invert (exact oposite)sound, effectively cancelling the oustside noise. (Graphicaly: uuu + nnn = --- )
They work particularely with the lower frequencies such as airplane, trafic, dishwashers, airconditioners, etc, so you can listen at lower volumes comfortably. They dont realy work on human voices, so if youare trying to block out children, it won't work
They have no effect on the sound in the recording.
They would not be very good for the deeper levels of the holosync program, simply because the frequency response of these headphones is no wider than regular headphones. They will be fine for the holosync in the paraliminals.