υἱὲ Ταντάλου, σὲ δέ: The effect of δέ after the vocative is to give pause. It is not uncommon in Pindar, and is used where γάρ would seem more natural, δέ=δή. Cf. O. 6.12; 8, 15; P. 10.10 al.
σὲ . . . φθέγξομαι: The position shows that σέ is not felt as the object of ἁρπάσαι (v. 41) until ἁρπάσαι is reached, when the impression is renewed. “Touching thee I will utter what wars with earlier bards.”