powergyoza asked the right question. Can air heated by the hard drives, by the Northbridge, the ram, the video card, the CPU, etc. still be useful.....useful enough to cool the PSU? And the answer is Yes, if the temperature of that air is low enough. On my own system described above, the output temp of my modded Fortron, the only output, maxes at about 36c. And that is after cooling the PSU. I find that temp perfectly acceptable. For you non-believers...well you'll just have to try it.
This airflow thing is difficult to explain, as there are so many variables. Basically for maximum quietness, the airflow through your computer should be tweaked for maximum usefulness. To me that tweaking process differs from the norm. Take a look at this picture
. This is your standard case setup....a CPU fan blowing down, a rear case fan blowing out, and a PSU sucking air......all trying to get this air from one small space. An ideal setup? Not to me.
Try this experiment....Take two fans, blowing them in different directions. Then move the rear of these fans closer and closer together. What happens? Well the output of each fan diminishes, and the noise level goes up. This is what is happening to the airflow from the fans in the picture, of course not as dramatic as the experiment. But the effects of restricted airflow are still there.
That is why I think a one fan setup could be superior. My setup may not be perfect yet, but I'm still tweaking it....and right now it works just fine.