I understand, Gerwin

Right now I'm listening to 4 fans-PSU, GF4, chipset, and CPU----ohhhhhhhhh do I understand. My parts are comming next week, and I'll be in your shoes. I'm using a big bucket until I can figure out the best way to passive cool- and copying you idea (if you don't mind?) has once again come to the top of my list. Anyway.
Watercooling a PSU seems a good idea to me. The pics you posted from low-noise.de look to be the best job I've seen done of it, but
digitalexplosion has an article about it.
I'm with gmat. Building you own case is in my mind the best way to get the maximum convection cooling to everything that needs it. I don't really like it, but
this guy did a pretty good job over at overclockers.com. From what I've seen around, Bladerunner just leaves his case totally open. No sides or anything at all, and I bet that works, but then you run into the loud Cuda HDs again.
I think it's about time someone put those thought into writing; for AMD to provide a stock HSF that produces 50db is simply crazy. Just bonkers. I think it's totally stupid that people who want to quiet down their computer are looked at funny, and have to go to GREAT lenghts to do so. Just little designing things, like a bigger CPU core, etc, would make it soooo much easier and better.