Has anyone tried tai chi to combat the effects of KD?

Yes, I practiced Tai Chi for several years and felt it really helped. As my legs weakened, I moved to Qigong and again felt it was very helpful. In fact, I put together a website after studying under Dr. Chung. The site can be found at the following link: Wisdom Qigong. I still practice a modified version today even though I can no longer perform many of the standing postures. Give it a try and let me know how it goes.