I do feel for you - it's a common problem these days as the XF is seen to be a 'large engined car'. I guess that most people seem to think that a 1.8/2.0 is extravagant so a 3.2 just blows their minds, add in the Jezza Clarkson factor and it's not an easy sell. IMO you need to keep it for sale and just enjoy it until it goes - as the saying goes it only takes one interested person.

Good luck