ooh, I know what this is. You need to tell the soundcard a bit more 
about your speaker configuration by adding something in /etc/modprobe.d, 
we had this on the webbook but the other way round (the speakers 
wouldn't turn off when you plugged in the headphones)
http://webbookblog.com/keep-the-noise-down/
your option won't be the same as mine but the full list of available 
options is in the file you can read with this command:
zcat /usr/share/doc/alsa-base/driver/ALSA-Configuration.txt.gz |less
Alan.
Vic wrote:
>> At the risk of asking the obvious, have you run KMix?
>>     
>
> Yes.
>
>   
>> Also, is it all sound,
>> or just some.  For example, KDE notifications are quiet, but audio CDs
>> and DVD audio work.  Again, check with KMix, looking at the relevant
>> mixer input and output levels.
>>     
>
> At the moment, I'm only interested in what Amarok puts out. I can hear it
> through headphones, but not through the onboard speakers...
>
> Vic.
>
>
>