Did you try one SRM6 instead of SRM4+SRM2? I know it has more spread at "long" range, but having on launcher in the arm and the other in torso is not without issues too.
I've tried them both. The SRM6 in the torso does prevent you from losing SRM tubes if you lose an arm but the spread from the SRM6 and t he fact that the 4+2 combo has a faster refresh make it deadlier.
TBH i just sold my XL240 because it is a bad engine. XL235 is much better because you gain that 0,5 tons for ammo, and that's more damage!