Maybe this is similar to my issue when I connect to my HDMI TV: If I plug in my audio output (1/8" cable) before connecting the HDMI, I'll briefly see a "NO" symbol with the audio (something like this: https://josephhall.org/nqb2/media/blogs/nqb2/stuck-on-mute.j...).

The workaround I've been using is to disconnect the audio cable, wait a second or two, and reconnect the audio cable. After that, I can send audio to my receiver and video to the HDMI.