Mate, I've just tried two 1.5TB WD Green drives, and it was a no-go for me. My Pro Duo model is a Japanese one off ebay, but with a 3.10 version firmware. When I went to update the firmware I received a "ACP_STATE_FAILURE" message right at the very beginning, and got no further. Initially one of the drives had a NTFS partition on it, but after reading one of the messages above about having no partitions on the drives, I wiped that partition out and tried again. But I still got the same error message. So me thinks they aren't supported.