I've reached sector 8 a few times, though I have yet to destroy the final boss. Without a doubt the one factor that most affects my success right now is whether I get an enemy with a teleporter.
I invariably end up losing a crew member or two when I'm attacked, and I typically lose the fight as well once that's happened. I usually scramble my crew to the fight as fast as I can, but they only win when they outnumber the enemies and even then sometimes a friendly goes down (or if the enemy is in a 2-square room I can't even outnumber them).
Is there a tactic or technique that I'm missing here to make enemy away teams less horrible? Obviously a Mantis crew member helps when you can get one, but even that doesn't seem to give me much edge.