In the Audio and Video Settings dialog, I have two audio devices:

but the one I want is greyed out. What does this mean?

That is the one currently active. Check the Audio Hardware Setup tab to change it if needed.

The greyed out one doesn't appear in Audio Hardware Setup, only the HDMI one.

Did you change the profile?

Ah, it was set to the wrong profile! I'm sure I looked at that, but apparently I didn't try a profile that enabled the analogue stereo. Thanks!

I wonder if any hints or explanation could be put on the Device Preference page as to why items are greyed out?

Unfortunately it is not often clear to Phonon, the underlying Phonon backend or even Pulseaudio that the change in device is due to a different profile - so it would be difficult to provide this information i'm afraid.

Ah, OK.

Now I've worked out which profile I need, how do I set it as default? Currently the profile is lost on reboot, and I can't see any 'set as default' button.

There's a 'Defaults' and a 'Reset' button, but both have a tool tip saying they will reset (different) settings, and neither appear to do anything - at least, nothing in the UI changes when I press either button after changing a setting.

The profile getting lost on reboot is a bug in Pulseaudio, already reported in Launchpad.

OK, thanks. Do you have a link for the bug? I couldn't find it in Launchpad.

Please see here: https://bugs.launchpad.net/bugs/1236067