Yeah, I do the same. Soup sock in a vacuum cooker. It's the chinese way to make soup. The chicken does turn out dry. Perhaps it's worth taking the chicken mear out (leaving the bones) after an hour and adding it back after the soup is done.
I would rather have the real chicken aroma in the stock liquid, and I consider bland meat a sign of a successful extraction. Why would I want to stop that happening?
I find that trying to keep the natural flavour of chicken meat in soups is a fool's errand anyway. I don't know if it makes a difference, but if I'm returning the meat into soup I will separate it, put the pieces in a small tupperware along with a ton of chicken stock powder, and just enough water to cover. It then sits in the fridge until the soup is 10 minutes from ready.
