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The audio output does work now, but currently the MATRIX Voice audio output only works well for a 44100 Hz 16bit stereo output. So, in order to get it working, you would have to install the kernel modules as shown here.
Then, you would use the following command with the specified parameters to record audio using alsa for 5 seconds (adjust -d 5 to change this):
arecord recording.wav -f S16_LE -r 44100 -c 2 --vumeter=stereo -d 5
And the following command to play the audio using alsa:
aplay -D hw:2,1 ./recording.wav
You can check if your MATRIX Voice playback device is card 2, device 1 by typing the following in your terminal
You can also download audio samples from online & play them as referenced in this post.
Let us know if you have further questions!