The (originally 2-fan) power supply I have now is the SX400. My previous one was a PP-403X, I think. Both said they could handle 40A. Antec's older PSU's were rated to 40A, but the newer ones only say 35-38A, since PSU's nowadays are built to accomodate high current on the 12V line. They might still work, though. The 400W Sparkle/Fortron
is also rated to 40A, but I've never used it.
I tried both ducted CPU fans in suck, both fans in blow, and one in each mode. I decided to leave the bottom CPU in blow mode (pulling air in and onto the heatsink) and the upper in suck mode (pushing air out of the case). This keeps the CPU's reasonably cool, and it helps get rid of the exhaust air. The other fan configurations caused trouble elsewhere in the computer. My VRM2 temperatures were going through the roof (90C, ouch!) when I had both fans sucking, and case temperatures (which I gauge by the DDR temps) went up several degrees when both fans were blowing. However, my configuration might not be the best one for you! I just got fed up with the stupid heatsink fan clips, and so I'm done tinkering.
To install the ducts, I cut a piece of vinyl duct, jammed one end through the cut-away fan grill in the back of the case, and wrapped the other end around the CPU fan. I'm using SK-7 heatsinks, so the fan clips go over the end of the duct to hold it in place. It's a real pain to get those clips in place.
I have no fans on the back of the case to assist the CPU fans. Case fans do help, though: when I removed the case fans from a cardboard ducting experiment, I had to raise the voltage of the CPU fans by 0.5-1V to bring the temperatures back down to where they were before. But since the CPU fans are buried inside the case, they don't make much noise, so I left the case fans out.
All fans are 80mm Panaflo L1a, rotated 90 degrees, because they make the least amount of noise when their label reads from bottom to top. Here are my fan voltages: 5V decouple-mounted in the lower-front, blowing on the suspended SP1614N hard drive (temperature: 31C). 5V mounted with a Zalman fan bracket over the Geforce3 video card, whose heatsink has been replaced with a big copper thing (temperature: luke-warm to warm, never more than 50C). The CPU fans are wired through a Fanmate, and I usually leave the blow-fan at 6.5V and the suck-fan at 7.25V. This gives me idle CPU temperatures of 56C and 59C, respectively. (Wow, the Panaflo is really good at blowing air straight down!) Load temperatures when encoding a bunch of MP3's, two-at-a-time, are something like 59C and 63C. Raising the fan voltages by 1-1.5V brings load temperatures back to idle levels. All temperatures are read though Tyan System Monitor, and ambient temperature is about 23C.
The PSU fan runs at 6.5V, wired through a Fanmate and plugged into the motherboard. The fan is mounted on rubber thingies on the outside of the PSU, with no grill, and any air gaps between the fan and the PSU covered with electrical tape. The PSU fan circuit is useless in my model, since it ramps up to 11.5V after 10 minutes, no matter what I do. The fan circuit in the Sonata's PSU, and perhaps the one in Antec's other new models, is more sensible, and it might be worth using. The PSU exhaust air temperature varies wildly from 30C to 45C, depending on where I place the temp probe and whether I'm loading the system. A good way to test the PSU temperature is to put your hand on the top of the PSU's case: if it's hot, you need more airflow.
But the Antec PSU's are pretty durable: I almost burned my hand on it once when I forgot to plug the fan in!
My computer setup probably isn't ideal for you. It's not very pretty-looking, it is custom-tailored to my case, and it makes compromises that you may not be comfortable with. I hope I've given you some ideas, though.
If you do buy another PSU, I really hope it works! Before you make another purchase, try disconnecting individual components from your computer: the hard drives, the video card, the other expansion peripherals. Maybe even remove one of the CPU's. A certain component could be giving your PSU trouble. There's a thread or two on SPCR about Barracuda's causing PSU's to whine or buzz, for example.
Good luck! Thanks for reading this far!