Ipandrews, please don't mind me getting a little overexcited on the shadow killer, it's just your project made me discover what babylon 5 was, and I truly think of it as fascinating. I'm not saying though that you haven't already given it your best, and if you did fail (for now, that is), it is likely I will not succeed (especially since I don't know anything about fredding, yet). But perhaps it could be done, even if it meant to segment the mission in several parts, say:
part 1: you approach the planet killer and "see" it from afar.
Part 2: You are inside the planet killer (you past the sections), there fore you are in the midst (we could eventually organise for atray shots firing from everywhere (without seein the turrets): that would make surviving a certain task.
part 3: the core (unsure how this one looks)...
part 4: you are outside dealing with the rest of the drakh fleet while the killer blows and turns "supernova".
And eventually a few sequences to bridge the gaps.
(of course that's only an idea).