Manually Installing I2S Digital Audio

 This will work on the Zega Mame Gear, Mame Boy+ and Mame Boy Advance SP Kits

Step 1.

Run the following from your Raspberry Pi with Internet connectivity

sudo nano /etc/modprobe.d/raspi-blacklist.conf

If the file is empty, just skip this step
However, if you see the following lines:

blacklist i2c-bcm2708
blacklist snd-soc-pcm512x
blacklist snd-soc-wm8804

Update the lines by putting a # before each line

Save your changes

Disable headphone audio (if it's set)

Edit the raspi modules list with ...

sudo nano /etc/modules

If the file is empty, just skip this step
However, if you see the following line:  

snd_bcm2835

Put a # in front of it

... and save the changes

Create asound.conf file

Edit the raspi modules list with

sudo nano /etc/asound.conf

This file should be blank!

Copy and paste the following text into the file

pcm.speakerbonnet {  
   type hw card 0
}

pcm.dmixer {
   type dmix
   ipc_key 1024
   ipc_perm 0666
   slave {
     pcm "speakerbonnet"
     period_time 0
     period_size 1024
     buffer_size 8192
     rate 44100
     channels 2
   }
}

ctl.dmixer {
    type hw card 0
}

pcm.softvol {
    type softvol
    slave.pcm "dmixer"
    control.name "PCM"
    control.card 0
}

ctl.softvol {
    type hw card 0
}

pcm.!default {
    type             plug
    slave.pcm       "softvol"
}

Save the file as usual

Add Device Tree Overlay

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sudo nano /boot/config.txt

And scroll down to the bottom. If you see a line that says:

dtparam=audio=on

Disable it by putting a # in front. Then add: ...

dtoverlay=max98357a

Save the file and reboot your Pi with

sudo reboot