MAN-ATL is of course Delta's route of over two and a half decades given to VS on the A333 whilst DL focuses more ageing yet refurbished B763s into LHR. (That's ironic!)
MAN-LAX would be more point to point than spoke to hub like ATL and JFK are. Also the A330-300 is rarely flown on UK-West coast as it lacks range although the later models do better so perhaps good enough for Virgin? Can someone confirm if a VS A333 is a likely candidate or are we more likely to see a DL B763? Seems odd to do LAX before JFK comes back IMHO.