The HDMI does indeed support the audio input on this monitor. The 1/8" jack is for use with the VGA. I have a slew of these monitors and there seems to be a syncing issue with Intel HD graphics via HDMI / Display Port. It seems to work fine with AMD graphics. Will update the bios on PC, but as of now the latest monitor driver and display driver do not resolve this issue.
PCs with issue: OptiPlex 3020