The Zix is too chaotic and unpredictable a creature to join the master's ranks, and it is too powerful to leave unchecked. However, it may still prove useful.
It is bound to these ruins with Ayleid magic, with a single Welkynd Stone as the focus for the binding spell. I've shown a priest of one of the local Goblin tribes how to fashion totems using fragments of this Stone. There's enough power in the fragment to put on a light show, which is enough for the simple creature to worship.
In actuality, the totems will maintain but weaken the binding spell. Zix will be unable to threaten us, but will have just enough power to distract the Bretons. And a distracted enemy is a weakened enemy.