Are you sure that the house is wired for MasterLink, not Master Control Link? A single 8-pin DIN socket just might be the original MCL for a BeoLab 3500/LCS-9000.
If, we're sure that it's all ML, then that is definitely a PL socket, the question becomes 'Why?"
We kid because we love.
Bang & Olufsen Tysons Galleria
McLean, VA USA