On the mac, when you plug in the Quad in Upgrade mode (While holding >|| during power on), the drive immediately disconnects itself and Mac OS complains it was not disconnected properly. This then continues happening over and over in an infinite loop.
The mac automatically creates an invisible dotfile containing metadata on any volume it mounts. Since the Quad firmware upgrade procedure involves rebooting after a single file has been copied onto the drive, I bet the dotfile Mac OS writes to the drive triggers the upgrade logic in some way. Instead of just waiting for the first file to be copied to the drive, it should also ignore any dotfiles written to the drive.