Looking from the perspective of the 4 ultimate realities, as LayDhammaFollower pointed out:
cittā-cetasika-rūpa-nibbanā
… I wonder if we can think of the technical similarities / differences like this:
asanna realm = rupā only, no nibbanā
and rupā = hadaya vatthu + cakkhu pasada rupa + sota pasada rupa, from what we learned about brahmā in the rupavacara realms.
… and although there are hadaya vatthu and 2 pasada rupā, no cittā and cetasikā arise from them.
sannavedayita nirodha samapatti = rupa (jīvitindriya) + nibbanā
So, in either case there are no vedana and sanna, and the similarity stops here. Asanna realm is fully in this world of 31 realms; nirodha samapatti is in “between” this world and parinibbana.
Another speculation about the difference between the 2:
Elsewhere on the site we have likened asanna realm as being under anesthesia. When we wake from anesthesia we don’t remember anything, as if that time didn’t exist. I unfortunately knew this quite well, since I had been “under” the knife a number of times in my life; no recollection whatsoever of what happened in between.
On the other hand, if an aharant got into nirodha samapatti, for any duration, I doubt that he/she would EVER forget it. There must be some quality of “wakefulness” in this “experience”.
Best,
Lang