Do they always send 9 ships through? If so you could adjust the amount of mines so that maybe 1 or 2 will be crippled enough for you to easily capture. Don't try to kill them all
In my current game I've gotten quite a few Cue Cappa BB's with Alligience Converters this way. The mines took out their engines and shields, all their weapons remained intact for some reason. I just went in and captured them, cost me a few small capture ships in closing but I now have a small Psychic battlegroup without the ability.