I wonder if the double IGs might be one of the lists that could go after Xizor first. With the HLC(s), you can overwhelm his ability to deflect incoming fire, especially if he doesn't have a focus.
I actually considered it for a few moments before our initial engagement, knowing that the Z's weren't really a threat outside of Range 1. Here's the trick, though: I'm betting it all on my ability to get past Xizor's green dice.
Let's say that I am able to finagle a good enough roll and land 4 hits with the HLC. Let's also assume that Xizor has a focus on defense - because with FCS he may not always need it on offense - so he should, statistically, come up with at least a couple of evades, so I punch a couple of damage through. You'll shake one of those off to an adjacent Z and take a damage. The Mangler will have a slightly harder time breaking through, but let's assume a similar result since it would be firing second and you've probably burned your focus token. Again, you take a point and shrug one off. For all that effort, I very likely could have removed one of your Z's from the board and have less incoming fire to defend against.
For IG, it's about thinning the herd. The fewer shots he has coming in, the more likely he is to have tokens to generate misses or arcs he can get out of. Killing Z's off is what I want to do, and it is probably what you would rather me do as it leaves your most dangerous piece on the board, untouched and free to act as he wishes. Those green dice on the StarViper simply make it more likely that some of my damage will be negated, and what isn't will end up dealt to a target of your choosing, not mine.
Now, if I were running a mini-swarm of my own, I would probably play that match very differently. I have incentive to gun for Xizor in that match, as the more dice I throw at him, the more likely he is to fold early. But with only 2 guns to point at you each round and flying a ship that is allergic to large numbers of enemies, killing the Z's and weathering the damage that Xizor throws at me is probably my best play. That's not to say if you made a mistake and hung him out where I could get him I wouldn't take the shot, only that as long as you are flying him the way you should, it's not in my best interests to shoot at him until I've shot down a significant portion of his meatshields.