I haven't worked with Exchange for about ten years, but looking for information on the DisplayAttendeesAll, it seems to be a collection of objects. Only the names are displayed by the default view. Have you looked at the individual attendees in the "attendees" property of the calendar item? I think they are recipient objects. If they are they should have the LegagyExchangeDN, SMTP address, and RecipientTypeDetails.
All of that's unverifiable by me, though. I used to be an Exchange MVP for 16 years, though (before retiring), so it might be worthwhile taking a look.
If I'm wrong, try looking at the calendar item itself.