That did the trick, uninstall IMP using the install script to do the uninstall.
Check all the sound was working as expected and it was
Reinstall of imp and I have audio goodness coming out of my Arcade Machine again :)

@o0mr-robot0o said in Audio devices not found.:

it's soldered to a custom pcb that holds the compute module etc.

If you replaced the CM with the 3b+ board, I wouldn't expect this to still work.

Should I edit that line to "yes"?

Sure, why not, but I don't see how it would work if you don't connect any of the audio outputs from the 3b+ to your device's speakers.

@rc_cola
Once when I experienced problems with cd tracks on psx games, I experimented with different audio drivers. If you dig more and search the web, you will find some different opinions. I think one of the audio driver will synchronize with video and if you get frame drops or anything else can't keep it up, then audio starts to stutter. Changing the driver did resolve this problem, if i remember right. The audio wasn't no longer synchronized, but it sounded without problems and I couldn't tell anything wrong with it. It was only happening with cd tracks. So, in short, this could be one of the tradeoffs. I have no more details about this, sorry.

Btw, you may find more information if you search about these topics in generell, like sdl vs alsa. These are common in Linux. And just in case you missed this page:
https://retropie.org.uk/docs/Sound-Issues/ Note, they speak about older Raspberry Pi versions on this page.