Here is the Greek for 1 Tim 3.16:
Ὃς ἐφανερώθη ἐν σαρκί,
ἐδικαιώθη ἐν πνεύματι,
ἐκηρύχθη ἐν ἔθνεσιν,
ἐπιστεύθη ἐν κόσμῳ,
ἀνελήμφθη ἐν δόξῃ.
The NRSV translates it like this: He was revealed in the flesh, vindicate in spirit, seen by angels, proclaimed among Gentiles, believed in throughout the world, taken up in glory. This is alright as it goes, I suppose, but I would translate the first three lines differently myself.
I agree that the first line speaks of Christ's revelation in the flesh. Here the emphasis is on Christ's humanity, on the truth that he has a body and a human nature as much as I do. Indeed, as the ancient dictum says, What is not assumed is not healed. If Christ did not take on a human nature such as my own, subject to all the same weaknesses as my own, and in its entirety, then there is an aspect of my being that goes unhealed. I might press the point, too, that to speak of Christ's being revealed in the flesh presupposes a kind of preexistence: you hardly reveal something by creating it ex nihilo; you reveal what already exists. There are numerous parallels between Christ and God in the letter to Timothy: Christ is called Savior (1.15) and God is too (2.3); Christ gave himself for all people (2.5-6) and God desires all people to be saved (2.4) and actually is the savior of all people (4.10). So Christ's revelation in the flesh carries a note of incarnation.
As for the second line -- ἐδικαιώθη ἐν πνεύματι -- here there is room for interpretation. Of course much depends on how we interpret Paul's use of the verb δικαιόω and related forms. In this respect I especially appreciate Douglas Campbell's argumentation in The Deliverance of God, interpreting the verb and related forms as referring more to a deliverance than anything else. If we follow him on this point, then we can interpret the passive aorist form in this line like this: Christ was delivered by the Spirit from death, echoing Rom 1.4.
As for the being seen by angels, I think the reference may be less to angelic creatures than to messengers, that is, the messengers of the gospel. The word ἄγγελος refers to angels but also in general to a messenger, a person who brings a messenger of some sort. I think Paul's reference is the same apologetic one he makes in other contexts (e.g., 1 Cor 15), and which may have been a repeated point of early Christian gospel preaching: Christ was resurrected from the dead and he appeared to us who are telling you all this. It's not immediately obvious to me why Christ's being seen by angels would be something to repeat or sing about, but I can see why they might have sung about his appearance to the ones who would take the gospel forward.
So, here's my revised (looser at points) translation of 1 Tim 3.16:
He was revealed in the incarnation,
Delivered by the Spirit,
Seen by his messengers,
Proclaimed among the Gentiles,
Believed in throughout the world,
Taken up in glory!