I saw this after using the Innomaker instructions as a guide. Thanks - it all works for my Rasp Pi 5 with the addition of (comma) ,slave to the end of the dtoverlay like so:-
dtoverlay=allo-boss-dac-pcm512x-audio,slave
The Pi5 has issues with I2S and this overlay fixes that.
I am not using Plexamp but have LMS set up on a Pi4, by installing Squeezelite on the Pi5, LMS can see the Pi5 as a player.