Package: installation-guide Version: 20150528 en/hardware/supported/arm.xml says:
[..] Support for the onboard audio options (analog, S/PDIF, HDMI-Audio) and for the onboard WLAN/Bluetooth module is not available in &debian; 8. I don't know if this is true or not but in the case the Debian 9 install guide shouldn't refer to Debian 8. -- Martin Michlmayr http://www.cyrius.com/