Hi,
These are actually Audio In's on the C10 however during production they were originally connected to the analogue output.
Its not a supported audio source, and to be honest the audio was a direct feed from the motherboard, which could have issues like clicks and pops as the software did not have any control over how the output was being fed.
It is not a supported method of connection.
Also on further firmware builds the feature may get turned off altogether.
The C15 did not have these connectors as any feature that would require them was not moved forward.
Regards
Edd