Debian 9.0.0 installed fine on the M.2 SSD of my shiny new Udoo X86, and the video performance in firefox 52.2.0 leaves my old host for dead - but there's no audio on the HDMI, either with HDMI cable or HDMI to VGA adaptor + stereo audio cable. (Monitor switched to HDMI vs VGA, to suit, as confirmed by video working fine.) Clicking on "Sound & Video" -> "PulseAudio Volume Control" menu item, and setting "Firefox AudioStream" to 100% (0dB) still delivers only utter silence. And yet the VU-meter bar under that control is flapping about vigorously, so there's audio coming from firefox - it's just stuck in there. The "Output Devices" tab provides two options at "Port": Speakers Headphones (unplugged) but just confirms that the audio component of HDMI is implicit, hopefully. The monitor's volume control is set to 60%, as 100% of even 2.5 W/channel would be a bit much, once we clear the dead rat in the audio plumbing. But where can it be? P.S. An aside: Don't try to install from a debian "Live" .iso - that locks up in an endless loop, insisting on finding a CDROM.