I actually don't think it's necessary to use fans at the base of the unit - if you have a fan (or fans) blowing air out of the access hole, with the appropriate intake area you'll suck sufficient air in through all available apertures. As a very rough rule of thumb, the total cross sectional area of the gaps available to suck air into the cabinet should match your exhaust "hole", so in your case, the sum of all the gaps around the doors would need to be roughly 400 sq. cm. Ideally, you'll want to make a seal around the exhaust fans so that you are actually drawing air across the units - without a reasonable seal, the fans will just suck a lot of air in using the path of least resistance, which could easily be from immediately adjacent to the actual fan unit. What you need to make sure is that air is actually drawn across the units you want to cool - if air can get sucked into cabinet and exhausted without actually passing over/around the equipment, it won't do you any good.
I couldn't quite tell from the two diagrams, but ideally the access hole you're going to use as the exhaust port should be as high in the cabinet as possible, otherwise you'll end up with a 'puddle' of hot air above the stream of cooler air.
Another consideration is to make sure there's good vertical air flow between each piece of equipment, again, you don't want to a pocket of trapped hot air. And just to offer a slightly different perspective to PSUMazda, if the shelves are preventing the natural upward flow of air, you may be better served my removing them (stacking the units with greatest heat output - like amps - on the top). Also, what you don't want is cooler air coming into the cabinet lower down and just shooting up the gap between the shelf and the back of the cabinet before being exhausted - putting strategically placed holes in the shelves is one way of managing the path that the cooling air takes through the cabinet.