ReadyNAS Pro compatible CPU Coolers
I tested 3rd party CPU coolers compatibility on my Pro 6:
Both need some dirty work, to use the screws, need to push away the fins with the screwdriver. Not nice, but working.:
Scythe Kodati : compatible (1-1.2cm left over it). You can use a 2nd fan on the top (80x80x10mm), but not help.
Alpenföhn Silvretta : compatible (3-4mm left over it). No more place for a mosquito even. No place for a normal 92x92x25mm fan, only 15mm thin working. Noctua NF-A9x14 PWM example.
Here is a pics, with he twin Nortbridge coolers, now the NB is only 53celsius, not 62-65. Look ugly, but working.