Thanks,
I have now, and I can even get cmus to launch and 'play', but whatever I do with alsamixer I can't actually hear the output. I get a loud pop when the file starts to play but nothing else.
I was previously using Puppy Linux on this old machine but it took so long to boot I decided to try something else, so I know it was working until now. I expect there's something missing I need to install or initialise. I've already discovered dependencies don't always get picked up.