Octavia audio unit. CD issues.

It has this audio (see pic) unit fitted. There appear to be different variations on a theme so don't know which model number this is, anyway:-

1) It has swallowed a CD then, almost immediately said it was ejecting it, but didn't and no amount of button pushing has resolved the issue so have notionally lost a CD disc, at least for the moment.

2) There is a CD Multichanger (which is on the car's specs).  It will load and eject discs, so no problem there.  The issue is that the Multichanger is not being recognised at the audio unit.

3) The HDD has a number of playlist items loaded (totaling 0.35GB out of 18.62GB) and one can delete them but, there is no indication of how to load new ones unless,  of course, that would be from an SD card.

Thanks in advance for any help.

Nigel