You brought up an option I had not considered – the Yamaha DB25 is NOT compatible with the H8000, which you correctly identify as Tascam-type.
Your snakes may or may not work, depending if they are Yamaha or Tascam types.It sounds like they are analog versions, so probably not useful..
Routing options rather depend on what you are trying to do. I'd start with one of the AES8 types.
It sounds as if the best thing for you would be a Yamaha to 4M/4F XLR. These appear to be available from various sources. Then, to connect to the H8000 you need a Tascam to 4M/4F XLR. Just connect the male XLRs to females and you are in business.
