How to 6I24-16 and step/dir

I'm currently planning my next retrofit. To avoid network problems I'm thinking about a Mesa 6I24-16 or 6I24-25 card. At the moment I see 2 questions. 1. How is it possible to create a step/dir and encoder connection with the card? 2. And what is the difference between these cards?

For a 6I24, you could use a 7I52S daughtercard to get 6 encoders + 6 differential step/dir channels
Or you could use a 6I25 and a 7I85S to get 4 of each