Now, you will have enough time to prepare the bomb and attempt to defeat the Star League. You're not going to wage a traditional war on them, taking their star systems one by one. That would be immensely retarded given your strict deadline and take years. No, a simple leak of information, a half-truth claiming that you have a weapon that can destroy the defense drones - perhaps a bomb of some sort - will cause them to act quickly before you grow any stronger. They might mobilize for Earth, but once they notice your entire fleet moving towards the gateway they will have no choice but to engage you in battle, and the presence of the Imperial fleet practically ensures that they're forced to throw everything they have in your way to have a chance to stop you. You will then attempt to crush each other in a series of fleet engagements leading towards the galactic core.
Remember, the League's immortal Council is not interested in ruling the galaxy or even the universe - not by sheer force of arms at any rate. They want to meet their gods over anything else, they've spent thousands of years working towards it, and it is that psychological weakness that Senya plans to exploit in B. There is no point in them attacking Earth if you are going to reach the portal first.
The criteria for being the winning civilization is actually to just reach the gateway, but due to the unsurmountable difficulty posed in getting past the defense grid - which also serves to prevent the first civ from merely being the luckiest by virtue of starting position - it is generally much easier to just stomp or assimilate every other culture out there - which is what the Masters intended for their game. However, any civilization strong enough to bypass their defenses would be strong enough to win outright should they make an effort to do so, and so it makes no real difference to them in that aspect - the first one to reach would still be considered worthy and they would be rather short-sighted to reject them for that. Thus, if you appear to have figured out a way to bypass the drones, you will have the League's undivided attention.
And in B, you want that. You want them to commit everything they have against you so that you can smash them down at the height of their power and leave them utterly beaten and lost, that there is no doubt that you are the victor.
Given what I just said, you might think 3C is more conducive to dialogue with the Masters. And you would be right; they'd be friendly(er).
Still, a reminder of the current circumstances: You entered a mind pact to invade the Masters' home dimension. Now, that doesn't mean you absolutely have to win. You'll at least be expected to make an effort to pillage a little, burn some buildings down, kill a Master or two. Blowing up their dimension satisfies Adrahasis, as mentioned in the update - and also because it necessitates an operation to enter the portal to set the bomb - but that doesn't mean you can half-ass it and pretend talking to them and then buggering off is considered an invasion.
But some of you might want to take the risk of the mind pact triggering and frying your brain, hoping for a reset after you've drunk up the infodump and can make a different, more informed call, so there's that tactic too.
