I was wondering why you wanted to put an NVidia card into a Crossfire enabled board? Nothing wrong with that, I have an ATI video card in an SLI enabled board. But, like me, you won't be able to upgrade by adding a second card. OTOH, my son's computer has a 7600GT and he gloats about it being faster than my AIW X600Pro and has an upgrade path to even better performance by adding a second card in SLI.
My ASUS A8N-SLI Premium has similar passive cooling and was well worth the money. Combined with the Sonata II it is virtually silent. Way below ambient noise: refrigerator, forced air, etc.
GDX made some good observations about the Sonata II. The CPU duct is pretty imposing. Fortunately it did fit over the rather low profile of the Zalman CP7000 fan. However, the duct opening is square and I wonder if it couldn't have fit over the stock AMD cooler and isolate the fan noise? My tower sits on the floor and vacuums in a lot of dust through the low front vent that cakes the CPU fan. I'm hoping the duct will prevent that because it draws air from the rear of the case about 10" above the floor. If not, it's going to be a bugger to remove to clean the CPU fan. Definitely, disconnect the blue front panel LEDs. My wife hated them and isn't too keen about the PWR & HDD lights blinking either.
One last thing. You'll love that dual-core CPU. My Athlon 64 X2 3800 simply blew away my previous Athlon 64 3200. My son can play Prince of Persia while MCE is recording a TV show with absolutely no dropped frames!