Well the behaviour of Linux on my Mac seems to be fast, but at times confusing. After some googling there was some indication that the problem with a lack of sound might be headphone specific. Sure enough, unplugging the headphones meant that I got sound (when this first happened it was a YouTube video at full blast). There doesn’t seem to be much logic to the thing, clicking mute and unmute on the various sound devices seems to lead to the sound working.
Unfortunately this isn’t really of much use to me. I share an office with others, and I don’t think they would appreciate either music or YouTube videos while we work. The effort continues.