Hi... My thoughts are two high speed PWM Be Quiet! 140mm intake fans on the front, and one 120mm in the rear. I have an extra 120mm and 140mm Fractal Design branded case fans, but i'm looking for a quiet build and i'm not sure they will be quiet enough.
If you are ONLY looking for quiet fans, then most of the Be Quiet fans are fine for the average build. If you are looking for fans that are quiet AND can provide a very high performance level while STILL REMAINING quiet, then you probably want to scrap the idea of using Be Quiet and go with Noctua.
Noctua makes black models of all their most popular fans now as well, so you don't have to settle for earth tone colors just to get fans that perform well.
What are the hardware specs going to be in this case, since obviously you've made a change from the Carbide 400R in your signature, so I have to assume other changes as well.