And Happy New Year to you as well…
You are entirely correct – doing what you are doing will not work. The H8000's DB25 connector is wired the same as the Digi, so if you just connect one to the other you are connecting input to input and output to output with the predictable (non) results.
Essentially to do what you want, you will need a "crossover" cable which is not usually available. In this case, I usually recommend buying two "Digi-snake" type cables, which are DB25 to 8 XLR, 4 male, 4 female. Then you can connect the male XLRs of one cable to the female XLRs of the other (and vice-versa) and everything will work.
The downside of this approach is that it is not cheap, but the flexibility it offers offsets this to some extent.
