Hi all, thanks again to everyone who has offered advice etc.
Just a quick update: I got an email from the lost and found on Saturday saying they hadn't found the headphones.
I was in Amsterdam over the weekend and I asked the cabin crew what happened with things left on the plane. They said they would drop them off with the transfer desk. Anyway I asked at the service desk again who told me that the airport no longer did daily rounds collecting lost items.
So I guess there is still hope but it is diminishing daily.