I'm sleeping right to my 3x CSE835's in one rack. Please stop trying to modify the Supermicro fans. I was on the same path for months and not successful. I was experimenting with lots of fans, controllers, motherboards to turn down the rpm's, keep the noise down, keep the temps of the HDD's down, and even more important, keep the components (motherboard, PCIe cards, Ram, CPU's, etc) cool. If you stick with the original design of the Supermicro cases, you will just lose time, money, patience, and more important .... you will fail long-term.
If you do not start to get rid of the original fan wall, just don't think about trying to lowering the fan noise without running into other significant issues. Either you will get the noise down, but HDD temps will rise. With rising HDD temps, your temps of the air inside the case will rise disproportionately. So your Raid-card will heat up, your CPU will heat up. This is a circle you can't win without noise.
Solution:
Get rid of the original fan wall. Buy some sport-hard-foam from Amazon or eBay, get a cutter-knife, buy two Noctua 120mm (1700rpm) fans. Don't buy the Industrial-version. At least mine had a whining sound. If you have room temps like I have around 25%. put the Noctuas at 75%. Otherwise less. But the higher rpm the better it is, the cooler the HDD's run and the cooler the air blown by the fans. They are still silent. No worries. I'm currently designing a front before the cages to cool the HDDs there so the air is cooler coming in the case and rpms can be even lower. But, the most important thing is, getting the hot air in the case quicker out than it's coming in. For this, I use 2x 80mm and 1x 92mm high rpm Noctua or Arctic fans running 80-100%. Still, can barely hear them. If possible clean up your case. Stick cable on the case wall wherever you can. Any turbulence causes noise. If you want to go ridiculous, put noise dumping tape inside.
Yes, 920SQ PSU's are mandatory.
So your best friend to noise cancellation is your DIY hardware store right around the corner. Here some photos of one of my most heated-up cases. I can still nicely sleep right next to it (50cm away from my head).