Yeah, stock fans are never a good idea if you value silence.
First thing first, I find that http://www.silentpcreview.com
is a good resource for lots of things silent (cases, fans, CPU coolers, etc. etc). Good reviews, and great forums to ask for other people's personal experience with products.
Given that, my personal opinion is the following:
You've got a pretty decent case their for keeping things low-noise, and I suspect the included EarthWatts 500 PSU should also do a fair job of being "quieter". At 6000 RPMS, I'd definitely say your CPU cooler is the biggest source of noise.
In other words, you could change out the PSU, and even the case if you want, but start with the CPU cooler/fan combo and see how you feel. That's where your biggest change is going to come from.
Looking at the product page for your case, it looks like its 206mm wide. If we lop off 30mm to account for both sides of the case, and the motherboard standoff, I'd say you've got 170mm of room to play with. If you can find a HSF (heatsink/fan) setup that is ~165mm, ~160mm or less, I'd say you're good.
I've been a big fan of Thermalright (not Thermaltake) heatsinks for a while. I've used these Ultra120 tower heatsinks
in two of my builds with good results. Couple that with a big Nexus, Noctua or Scythe 120mm fan and you can get better cooling performance at ~1900rpms.
Of course, the Ultra120 line seems to be discontinued, but they have a bunch of successors it looks like (venemous?)
Anyways, that's my part suggestion. In general: you'll want to find a good heat sink that can accept a 120mm fan or bigger (remember, bigger blades means moving more air at slower RPM). Don't be afraid to buy a heatsink without a fan. Seperate heat sinks allow you to pick a fan of your choice to do the cooling.