I have an HDMI monitor plugged in and I can get sound to come out of the monitor's headphone jack, but I can't get sound out of the Rpi's onboard jack. I've tried changing the AUDIO_DEVICE_ID to 0, 1, and 2 in the samplerbox.py file... but none of them make the onboard jack work.

Thanks in advance for any help!

On another note, I did a manual install on a different SD card running Raspbian and I can't get ANY audio to work on that (from the HDMI monitor OR from the onboard jack)

Hmmmm

I have the same problem

I got it to work using this command

amixer cset numid=3 1

then I added that to the rc.local file, I think.