I disabled the fans and connected the miner to the air extraction system of the building. Also swapped out the APW7 for a normal desktop PSU. The miner is almost completely silent now.

With Braiins I underclocked the miner to 325 MHz, and I'm getting a hashrate of 6.5 / 7 Th/s with temperatures of 80 / 85 degrees Celcius. (When things heat up during summer I can go as low as 200 MHz.)

When playing around with the MHz I also noticed that the miner will still shutdown when --fan-dangerous-temp is reached, even when using --no-sensor-scan. (So a failing air extraction system will luckily not destory the miner.)

I'm very happy with Braiins, because before all the boards in this miner were considered to be dead because of the problems they had.