[TheWamp]

6 disintigrators, 11 darklances (since there's no hurry to get to the enemy you can't kill.

2 dark lances 4/3 hits 20/18 dead broadsides.

6 disintigrators, 4 hits 4/3 glancing hits 8/27 dead devilfishes
9 dark lances, 6 hits 3 glances 6/9 dead devilfishes

So one dead tau tank per turn assuming all the DE stay alive.

However, given how much tau firepower can be brought to bear, I'd say that those DE transports won't last and in this case that kills them, since the Tau just hop back in their tanks and move away.

I vote Tau