@bagoflaxia said in mpg123 player works fine for BGM, but kills game audio.:

Is there a command I can put in to the mpg123 config to stop this from happening?

There is a topic on how to set this up in RetroPie - https://retropie.org.uk/forum/topic/9133/quick-and-easy-guide-for-adding-music-to-emulatonstation-on-retropie-noob-friendly.

Follow the instructions in the topic and add the commands to stop mpg123 when a game starts by editing the runcommand-onstart.sh script, this should stop the music from playing while the game runs.