I think there are two issues here. The first is pressurizing your abdomen vs your head. keeping the pressure in your abdomen/chest (intra abdominal and intra thoracic pressure) is a skill that helps stabilize the spine and generate and maintain overall muscular tension. I wouldn't say there's any "trick" to it, but there's a skill to holding the pressure in more at the epiglottis level than with the mouth and nose.
The second is what you mean by "power breathing." From your description is sounds like you might be trying to generate pressure by trying to blow out against resistance, as if you were trying to blow up a balloon. This is directing the pressure up into the head, generating sinus pressure, instead of compressing it down into the abdomen. But my understanding of power breathing is that it isn't a way of generating or increasing intra abdominal pressure at all. If you wanted to maximize intra abdominal pressure you would just hold your breath throughout a lift (which is how a lot of people do lift). Prolonged breath-holding tends to cause a spike in blood pressure, followed by a drop in blood pressure, which is potentially hazardous. In Power to the People, Pavel felt the need for a disclaimer about talking to your doctor before holding your breath while lifting (although Pavel does advocate breath-holding as a technique).
Power breathing enables you to gradually release intra abdominal pressure while maintaining muscular tension, instead of abruptly relaxing. It's a way of exhaling while maintaining pressure and tension, not a way of increasing pressure and tension.
For instance, on a press, instead of holding your breath all the way to the top or relaxing and losing tension, once you get past the sticking point, you gradually release the pressure against resistance, making the "Tssss" sound with the tongue against the roof of the mouth (not allowing the pressure into the head and holding it back with compressed lips).