How about this: Give it six anti-cap beam cannons, somthing like 2 TerSlash and 4 LTerslash, or even just 4 Terslash. This sounds like a lot, but it depends really heavily on the arcs you choose to use. If they are arranged evenly around the ship to give it a good level of all-round defensive protection then it becomes very reasonable for a carrier. 4Terslash is the Deimos loadout, although the corvette is turreted in such a way that any target in its frontal half is always under fire from three beams.
I think a very reasonable loadout would be 4-6 light anti-cap beams, an equal number of AAA beams, and the rest being missiles and flak, with the beam cannons focused around the launch bays and the flak and missiles covering the flanks. Although I like the idea of giving it anti-cap missile launchers... a treb-armed carrier is a really neat idea because it can nullify the anti-fighter turrets of enemy heavies to let bombers do the actual killing job, and it can do it from outside the range of some beams.
