If you want to connect your tanks together you could place them side by side and use an airlocked waterbridge that would allow fish to swim up out of one tank and down into the other. I've seen a few that looked pretty neat.
I have to admit, I've been trying to think of how your idea in the pictures could work. If the top tank was sealed to prevent air escape, and there was a baffle extending down a few inches into the lower tank where it comes in from the upper tank, I can't say it won't work. There will be some counterbalancing forces in action. It's possible the upper tank could implode, instead of blowing out the lower tank. One of the problems, you would really need to be able to seperate the two tanks to do anything in the upper tank. And any air leak in the upper tank would cause the water to empty into the lower tank.
I really like the potential of your idea, but there are definate hurdles to overcome, and I wouldn't want to try it out with a couple large aquariums jury-rigged together in my living room.
"The important thing is not to stop questioning. Curiosity has its own reason for existing" A. Einstein
"Life is either a daring adventure or nothing."
"We can do anything we want to if we stick to it long enough." Helen Keller