Strategic Help required!

[Nitram Draw]

I never use Tachyon weapons as a main weapon. The problem with the Tachyon weapons is their short range. You have to stay close to be effective and in your situation close is not where you want to be.
I would try to take advantage of the situation the best possible way. I find if I am seriously out gunned then I feel am better off with lots a targets that do lesser amounts of damage. If the DN can only target 3 ships per turn have 15 small units attack it. At least you will get 4-5 turns of fire in. It may seem stupid to attack with escorts but if you don't have fighters then they are your best alternative.
From your post I don't think you have shield depleters but if you do use them with your capture ships. Even if you don't analyize any captured ships you will have some good ships to defend with.
You have a tough problem, you are seriously out teched. You need all the time you can get to even things out.