you should not ask HR at McKinsey or Bain to give you details about the interviewers beforehand. Simple reason is that the allocation is very often only done on the day of the interview (it depends on actual availability of interviewers). So asking HR for information before they have finalized logistics and planning would come across a bit weird I guess. At BCG, interview day planning is less "fluent" than at McKinsey, so giving you information on your interviewer is a defined part of their process. But this is not true for McK and Bain.