Long story, but we've already started talks on separation. How do you deal with a spouse's incessant anger? How do I respond productively? How do I encourage him to deal with his pain and to talk productively/be less toxic? How do we create the most peaceful environment for our daughter? I'm trying to get him to do counselling. I'm not sure what to do otherwise, except remaining calm and rational.
Encourage divorce counseling to help create the best situation for your daughter. If you approach it to him as being for her, it might go over better. I'm not sure on how to respond to his anger. Maybe acknowledging his feelings would work best? Remember in whatever discussions you have that "I" statements will always work better than pointing fingers. "I feel like I'm under attack" is always better than "you're always angry with me".
I agree you could encourage counselling, and it is not at all right for him to direct his anger at you. You need to keep in mind however that he will greive in the way he wants to, and in his own time, and may not want or accept need of help. There may be nothing you can do about that and you might just have to let him work through it.
It will be a long time until he accepts this. Maybe never. In the meantime, I don't think you are under any obligation to accept being treated with anger or even abuse. Does he see himself as a "victim?" If so, there is a little, if anything you can do to change his thinking. Only he can do that.