Would you be willing to answer a few brief questions about PlayStation Forums?
Just today, I solo'd Rotunda of Olypmus with a level 28 Posiedon.
War Hammer of Poseidon (Rank 1)
Full Manticore Set (Rank 2)
Posiedon's Crest (Rank 3)
Cloak of Boreas (Rank 3)
Relic of Sacrifice (Rank 3)
Yes, it's not even remotely the most ideal set up, but that's what I used.
Artemis set w/o helm and maul of poseidon is what im running now and it works pretty well imo.
That hammer does pretty impressive aoe dmg.