Nice job @bbqdt ! Did you completely remove the PSU fans? Have you measured the PSU temperature with that mod?
Currently my setup is: All fans still there, but I cut two square holes on the top cover with a dremel, and put two similar 120mm fans on it.
Forgot to mention: I think @kapone 's 6610 is a 24P non-PoE version and mine is with PoE, so there is a huge riser for the extra ports that significantly obstructs the airflow. Current plan is to hack it even harder (thinking about cutting on the front panel).
So I added two 120mm fans for the heatsinks, one directly above the ASIC (black), and one on the left (the CPU, chrome). It now runs significantly quieter, though not perfect. I think the ultimate solution would be a water-cooled solution, but I am very happy now :)
Thanks a lot, @fohdeesha ...
I realized that after taking one PSU apart and let the unit run for a minute :( Thanks all for the information that cooling the ASIC actually spins the fans down, will try probably next week or so with a dremel :)