Land on Vistig, capture and reverse engineer all the tech we find, bring down the mortality rate, while still increasing or stabilizing quality for cyborged ships, advance nanotech, take about a year too land on the the colony planet conquer it, then ship off with updated weapons, maybe build anitmatter weapons. Send 2 Omega ships, attack gun sites with antimatter, low yields of up to 100 kilotons at first, but more if it is needed, if the ship approaching is hostile abandon Vistig. Do not get in the ships way for the love of god. Antimatter attack first.
Do not dedicate too much force to Vistig, or the homeworld, because we don't want full death.
Also bombardment would be hard with no ships left.
Also using biotech, nanotech, and small computers, augment Mariners into supersoldiers low morality rate wanted, should be able to be used on masse, and begin a project on a totally lifeless moon, using grey goo build a computer out of a moon, next use this computer to defeat alliance computers, also choose an extraordinary citizen using a test of science and tactics, and upload him too the computer, this should result in an expotential increase in technology via the use of technological singularity, first ensure he is loyal of course. Use the new tech to beat the crap out off people. Finnally civilians shall be integrated if captured, let them maintain their culture and don't use force too keep them in line.