ὧν οἱ πατέρες καὶ ἐξ ὧν ὁ Χριστὸς τὸ κατὰ σάρκα > ὁ ὢν ἐπὶ πάντων > Θεὸς εὐλογητὸς εἰς τοὺς αἰῶνας ἀμήν.
Two different ways of taking ὁ ὢν ἐπὶ πάντων are generally discussed.
(1) ὁ ὢν ἐπὶ πάντων is a participle phrase with the participle functioning substantivally, and starting a new sentence.
(2) ὁ ὢν ἐπὶ πάντων is functioning attributively, in the second attributive position (ὁ Χριστὸς τὸ κατὰ σάρκα ὁ ὢν ἐπὶ πάντων); in other words there is an attributive use of the participle here.
IMHO option (2) is highly unlikely.