The concept seems sound and for me the WebUI worked perfectly all sounds test ok, I was using a set of PC speakers in the Pi 3 B+ 3.5mm jack.
Here are my steps.
1. On first switch on I got some sounds randomly in game play (no constant random sound)
2. On re-soldering the ICs the sounds were in the correct place not all played ("change gear" for example on Getaway) but I started getting a sound FX when it feels like it (The same sound FX every time)
3. On re-soldering the ICs again the sounds were in the correct place not all played ("change gear" for example on Getaway) but I now get 2 sound FX when it feels like it (The same sound FXs every time)
4. Found the 0v fault. Connected but the sound fault remains.
5. Replaced the 374 IC but the sound fault remains.
The pi for me anyway seems to be receiving fake signals to produce a sound (now 2 sounds)when it feels like it and missing out other sounds.
I have tried another pi so this is not it.
I am thinking that the missing 0v has damaged the ICs but its unlikely and I changed the 374 IC, I can only think there is an issue between the WPC connector to the ICs onto the pi 40 pin connector steve45 obviously does not manufacturer the boards and I am thinking the 0v area of the board is very close on multiple pads so it only takes a bit of solder mask to be missing for something to be grounded out.