We are running it on some 859 Pro+.
They have a Atom D525 CPU. All 8 bays work flawless.
Just create a USB stick with the 6.0.2 boot image. Plug it in and change the boot order in the bios.
Haven't tried yet to put it on the internal DOM.
Just installed 6.0 without problems on a QNAP 859 pro+.
DualCore D525 Atom, 2GB RAM, 2 GBit NIC, 8x SATA.
Works perfect, just had to change the bootorder in BIOS.