I had asked this before in the Rulesmaster's forum:
http://forum.mongoosepublishing.com/viewtopic.php?f=75&t=49919
(Scroll down towards the bottom)
There was no "Official" ruling however. I like keeping each line as a weapon system, even if they are in the same arc and the same weapon, as it allows more flexible use to defend with only some, and also to split against different targets is desired. In the case of Drones, I am still kind of undecided: If they all get combined then then there is only one ADD group. If kept separate, then technically you could run ADD systems out of ammo quickly by rolling against each "Attack" separately. I think what makes the most sense is to leave them as separate lines so that different targets could be attacked or different lines could be used for defense, but to combine any like weapons fired against the same target as a single group when using drones.