Hi Dan,
Its funny really - Xray seems to now have somewhat a 'cult' following!....it is nothing more than a slight depression in the seabed, about 2 NM SSW of Hengistbury Head, although it is an obvious feature in miles of otherwise pretty featureless bottom.
James and I discovered the mark about 2 years ago, and have had numerous big bass, rays, conger etc....
I would also hasten to add that Im pretty sure that if you fished anywhere in the vicinity for a length of time, catches would also be good - I think it is more a case of a concerted effort in one place makes it seem like a super mark!
Adam