Small update:
my bad, the linux hdparm command actually works and the drive spins down. It even spins down on shutdown!
So the BIOS and the controller itself is just fine.
Obviously the Windows drivers are the problem here.
I'll compare the current installed version and the newest availlable.
Installed the newest drivers 1.17.59.0 for jmicron controller (listed as gigabyte sata2 controller) over 1.17.55.0.
NO change.