Hello!I'm a newbie here,and also a SDA.
About Christ's nature, I believe Hebrews 2:11 left no doubt that He had a fallen nature,exactly like ours.
Hebrews 2:16 also says:"For verily He took not on Him the nature of angels;but He took on Him the seed of Abraham".How could he partake of Abraham's seed if He took on Him the nature of unfallen Adam?
The emphasis here is that he did not take on some exotic,sinless nature such as angels,or holy Adam might have had,but the same nature that Abraham's children possessed.
He was tempted in the same way we are,yet He never once yielded to or entertain sin.He was always totally pure,holy and undefiled.
He was born in the same flesh and nature we have so He could understand better our weaknesses,and be a merciful High Priest to us.