Ditch the beams. Go with 3 DHCs+1 torp, and 2 turrets+KCB. You'll do much more DPS. Beams make sense on large, slow moving ships that have a hard time keeping opponents in their targeting arcs. The Defiant doesn't have that problem. Plasma is king at the moment, and Romulan plasma is the king of the plasmas, since the 2 piece bonus gives you more damage, as well the embassy consoles.
That's a pretty good starting point for an escort build, and is exactly what I run on my Fleet Defiant. It really shines with the borg+romulan console though, so I'd try to get those ASAP if you don't have them already.