Announcements and system sounds with dmix

I like to create an extra Asla input channel, such that announcements and system sounds can be played. All this without disrupting the audio. Via the AAMPP, Alsa contribution snippet. I have added the parts to add a channel and dmixer. See below the snippet and the resulting total asound.conf.

The problem is, it does not work. The error: Failed to open ALSA … appears when the PLAY button is hit.

Has anyone experience with dmix and Volumio? Any suggestions to debug. Many thanks

The ALSA Snippet:
#-------------Test dmix----------
pcm.in {
type plug
slave.pcm “dmixer”
}

pcm.mix_in {
type plug
slave.pcm “dmixer”
}

pcm.dmixer {
type dmix
ipc_key 1024
ipc_perm 0666
slave {
pcm “dmixer_out” # Intermediate PCM to pass to dmixer_out
channels 2
period_time 0
period_size 1024
buffer_size 8192
rate 44100
}
}

pcm.dmixer_out {
type plug
slave.pcm “out”
}

#------------END Test dmix--------
asound.conf.zip (1 KB)