Maybe, just maybe, when the writer says "when He
again brings
the firstborn into the world", he is referring to Jesus returning to the world after having been resurrected as the firstborn from the dead, and after He was glorified with the glory He had previously had with the Father, before incarnating as a little lower than the angels, i.e. human.
Heb 2:5
For unto the angels hath he not put in subjection the world to come, whereof we speak.
Heb 2:6
But one in a certain place testified, saying, What is man, that thou art mindful of him? or the son of man, that thou visitest him?
Heb 2:7
Thou madest him a little lower than the angels; thou crownedst him with glory and honour, and didst set him over the works of thy hands:
Heb 2:8
Thou hast put all things in subjection under his feet. For in that he put all in subjection under him, he left nothing
that is not put under him. But now we see not yet all things put under him.
Heb 2:9
But we see Jesus, who was made a little lower than the angels for the suffering of death, crowned with glory and honour; that he by the grace of God should taste death for every man.
Heb 2:10
For it became him, for whom
are all things, and by whom
are all things, in bringing many sons unto glory, to make the captain of their salvation perfect through sufferings....
Heb 2:17
Wherefore
in all things it behoved him
to be made like unto his brethren, that he might be a merciful and faithful high priest in things
pertaining to God, to make reconciliation for the sins of the people.