Jem Aswad Senior Music EditorIt’s hard not to listen to DMX’s posthumous album “Exodus” — which the rapper completed just weeks before his death on April 9 — without feeling wistfulness, but there are many classic moments on the set.One in particular is a rare team-up between DMX’s fellow New York rappers Jay-Z and Nas, bringing three of the greatest MCs of all time — not to mention one of its legendary producers in album executive producer Swizz Beatz — on a single track.Over rich, thumping