Retrofitting analogue volume control

Look, we are talking about a DAB alarm radio, aren't we? If so, there's probably no need for all this FUD. A few extra ohms in series with the speaker isn't going to hurt anything.

If this was a hi-fi system, at worst you might be worrying about the reduction of damping of the loudspeaker (which would show up its natural resonance and therefore affect its frequency response). But even a high power audio amplifier should not suffer any damage whatsoever when driving into higher-than-normal impedances (including a complete open circuit).

Would you notice on DAB?

The only DAB I've heard one could *just* tell the difference in boiling mud noises between speech and music, the speech had pauses between sentances the music didn't...

Never mind Dave. You'll probably get AC mains out your way one day too. ;-)