Chapter 37: So to add what wants in female sex, the more to draw his love, and render me more equal, and perhaps, a thing not undesirable, sometime superior; for inferior who is free? – IX, 821-825
Séances as they are known in modern and popular media are smoke shows at best. Spirits don’t travel the plane of living and so living things have no possible way to connect to them. No amount of energy can make a spirit manifest on this plane and no normal person can view into the beyond accidentally.
The saddest truth about those claiming to have seen ghosts is that they are most likely Banshees or Hellhounds themselves who were never opened up to their Gifts.
What can be derived from this is that one has to be dead to make any sort of lasting impact on a place like Hell. Now, as a Banshee, one does not remain dead for long.
Being a Harbinger of Death is sort of a forever-deal, so being able to traverse the divide between the planes is somewhat of a prerequisite, and for that the Harbinger has to be alive for the most part.