[Q]

Your enemy has ships with PPB each giving a damage of 250kT, isn't it? You have crystalline technology with crystalline armor III each reflecting 15kT damage to your shields. So if you build ships with at least 17 crytalline armors, which certainly is possible with baseships you can't be hurt by his weapons. Use yourself either shield depleting weapons plus any potent normal weapon or nullspace weapon. Of course he soon will change his ship design and use other weapons, which will penetrate your crystalline armor, but you will get time, which you can use to destroy his colonies.