[quote]Many armors in this RP also include the classic "immune to firearms" sentence thus directly rendering modern infantry weapons useless.[/quote]

This only opens up the possibility of someone drifting into the roleplay and proclaiming that their fictional suits of armor are incapable of sustaining damage from traditional science fiction weaponry. Throwing around the "I" word is a rather dangerous slippery slope to start down. 

At the end of the day, your standard M4 carbine is identical to a longbow, a crossbow, a flintlock rifle, or a near-future railgun in principle (but not in mechanical function). While the rules for a DEW may be different, a handheld railgun is going to be constrained by Sir Issac Newton's tyranny, making the few merits that it retains somewhat moot and irrelevant if the creature firing it is incapable of withstanding the recoil that such an infantry arm will generate upon being fired. If people are going to hand-wave the issue of recoil away with a railgun, the same can be done for the firearm.

At any rate, I'm not using modern firearms for my faction, but it irks me when I see people writing off customary firearms as inherently useless in space opera settings.         

[quote]My beams being antimatter only give them a slight boost in comparison. X amount of antimatter can only interact with X amount of matter.[/quote]

The antimatter itself, at least from my perspective, isn't the problem, but the concept of an FTL positron beam strikes me as being over-the-top even for a space opera setting. Your standard graser, x-ray laser, or neutral particle accelerator is overpowered enough, but throwing matter at warp factor [insert random numerical value here] is a tad ludicrous.