I tend to agree with GreenAsJade on “So desu ne”. If “uh huh” sounds a bit impolite as a response to something an elder (or a 9p) said, “right…”, “indeed” or “I see” might be more appropriate depending on the situation. I’m not sure about “(or so) it seems”, but “wouldn’t you agree?” makes what is said before it too obvious to be your opinion, which you, as a moderator, would avoid doing in front of a 9p.
I believe learning Go is just like learning a foreign language. The more we learn, the more we realize how much we don’t know. For example on “so desu ne”, you need to know professional Go players are always referred to as ‘Sensei’ in all the contexts related to Go, so you need to use the polite form of the language for addressing the elders no matter how much the pro is younger than you are. So you, as an amateur, never say “so da ne” (informal version of So desu ne) to a pro even if you are an old guy and the pro is a young girl, unless you are good friends and there are no Go-related bystanders around.
More intricate is the relative seniority among pros, where pro ranks and the titles-held determine the seniority. Honinbo and honorally titles (that are held permanently) weigh more than regular titles. When you reach a dan level in learning Japanese, paying attention to what pro uses “so da ne” and other informal format of the language to whom will be interesting, as it could show who is holding what title at the moment. (Keep in mind the importance placed on this kind of protocol is slowly disappearing among younger generations.)
Cho Chikun is my hero. Not only he has been super strong for a long time, he also mastered a foreign language (Japanese was foreign to him) and is a tremendous entertainer.