DHCs for the Galaxy-X work in PvE, I wouldn't recommend relying on it in PvP, though. Single Cannons won' really make your experience more cruiser-like - Cruisers rely on broadsiding, with means you're using a wide arc directed to targets on starboard or port side. Cannons only have a small overlap in that arc with beams.
I wouldn't say that. My Excelsior is a 3x DBB, 1 Quantum Torp ship with a 16.5 turn rate with my tac. It does faily good damage in frontal fights, and I can usually keep most of my targets in front arc. I laso have an Engineer with 2xsingles, 2x DBB in the fronts as well . With good skills (RFC,BOetc) you can deal some damage, not as much as some escorts, but you also have more hp to survive a head on. Theres no reason to assume cruisers=broadside. You can set them up to do well in frontal and sides.
Galaxy-X's are less like to do frontals, but you dont have to rely on broadsides. Single cannons do have a 180' arc and rapid fire and other things can make them usefull along side a phaser lance, rapid fire doesnt count aginst the fire time of the phaser lance, so you can do both at the same time if you wanted to. I'd say tinket with it on tribble.
I run DHC on my galx, and they work fine, and I pvp lots with it.
Here is the deal, don't rely on them. Use them as an optional "hot" arc. If they are in front arc, let them have it. If they aren't, hit then with single cannons and beams. I don't use torpedoes, the burst damage isn't worth it in my mind. I can do plenty of damage without them, or its the Lance to finish off a stubborn enemy.
Pvp, just remember not to ever think your a dog fighter. Your a tank with slightly meaner than usual firepower at the cost of turn rate. Have guns pointing every direction, keep your shields up and use your big guns and Lance when the opportunity presents itself but don't press the issue against anything but a carrier
VA1 tac, GAL-X ; 2x beam array, 1x dual beam bank, 1x plasma torp, fwd ; 2x beam array, 1x plasma torp, 1x tricobalt torp aft, add vent warp plasma1. the thing to remember is it will never out turn an escort, don't even try, cloak [it has that remember?] pop weapon batt get close 4 or 5 km, drop cloak , lance, warp plasma bath, tricobalt on auto fire, hyd1 plasma torp also on auto fire , all do major dmg to anything not fast enough to manuver out of the way. works best on cruisers or larger targets, NOT CUBES ; any thing smaller than cruisers, same thing ,no lance, torp sprd 1 from fwd. you are resrticked to an lt tac and an ensign tac for boffs , that is the weakness you hav to work around, boff tac space pwrs; BFW1 HYD1 SPRD2