Seems to be a bit of confusion here about breathing into your gut.
First off, it only works properly if you are wearing a belt. The ONLY reason you should be wearing a belt is so that you can get your breath in properly. Its not there to make you look like you got ghetto swag. Thats what straps are for. You use a belt to give your gut something to press against.
Put on your belt. Stand in front of a mirror. Take a deep breath. If you do it normally, you will see your shoulders rise as air fills your chest and, by default, pushes your rib cage out and up. This is what you did when you were 10 (cough), trying to impress the girls at the local pool. It does nothing for your stability but looks good.
Now, do it again, watching the mirror. Instead of filling up your chest, as you take in the air, force it down and your gut out. You are not taking breath into your stomach. Or your diaphragm. You are taking in air so that the part of your body that expands to allow for the extra volume is not your upper chest but your gut.
Your upper chest and shoulders should look much the same, but your gut will be extended to a point where the belt holds you tight. You will feel your belt pressing against the gut and lower back.
Now, whats happening is that your lungs are separated from your stomach and other organs by your diaphragm, a sheet of muscle that expands and contracts to enable you to pull air into your lungs. Pull down and air is sucked into your lungs, push up and you breath out. Your lungs do very little to fill and empty, its all diaphragm. Instead of your lungs filling and pushing up against your upper chest, you fill your lungs and bear down so that the expansion needed is provided by your gut sitting on the other side of your diaphragm.
As I have said before, think of a wine barrel. The bands are there to allow the wooden staves to expand to the point where they press hard against the copper bands, forming a strong rigid unit.