I installed Windows 10 (April 18 update) on external SSD drive that can be selected on the iMac's startup. Run the Boot Camp Windows Support Software and everything is fine, Apple mouse & keyboard, except audio is missing. Windows 10 Device Manager app does not show any problems with the drivers such as yellow triangles or red crosses. In fact, when a video is played the green volumen bars in the audio device driver properties move but there is no sound at all.