Sixiang is by far the best TA I have ever had an an undergraduate. If you have him as a TA in your EALAC class, be sure to register for his section. He is brilliant, extensively knowledge, CLEAR, approachable, helpful and responsive to emails. He is also very engaging and knows how to facilitate a good discussion during discussion sections.
He gave a guest lecture one day during the semester, and I think most people agree that it was the best lecture of the whole semester. Everyone in our discussion loved him and honestly thought he should be the professor. Columbia should hire him as full-time faculty. As a grader, Sixiang is tough but fair, perhaps a little on the tougher side, but if you get individual help from him when you need it, grading should not be a problem.