Eh, just ignore these guys, they are fighting uphill battles against themselves.
My recommendation, do whatever you wanna do, if you aren't tearing up your system, it doesn't matter. Try placing one in the front, one in the back, both in the back, in the different positions and all and see what kind of results you get.
Personally, I have my box set up with 4 Vantec Stealths, and a Antec TuePower PSU. The only thing I hear is my CPU fan. the 4 of these stealths are more quiet than any one generic fan.
The problem with stealths is that to keep silent, they don't move as fast, and therefore, don't move air as well. That's why I have 4.
So, after my rambling, I suggest either replacing all of your fans with stealths, or stick to your two fans and find the best way to fit them.
But then again, your system is still safe when your CPU is in the area of 65 C. Just make sure you keep an eye on it if your room starts to get warm.