I managed to enter the Bios of my ReadyNAS Pro 6.
Right there i can choose the boot order and also change the fans to "Thermal control".
Xpenology starts out of the box without hassle and installing 5.1 Update 2 was no prob at all.
But....this damn CMOS reset.... when trying to do a scheduled power on
Running XPenology on ReadyNAS was a great experience, but no scheduled power on/off is a no go (for me!). So i gave up