Sorry for the delay in replying, Javierk!
Much of the newness came from an expansion of the MC's side of things: how to set up and run matrix systems. The other major change was in reducing the granularity of combat in the game entirely. Mix it Up has become more like seize by force (rather than DW's Hack and Slash), so instead of attacking harm clocks, I've gone back to a more conflict resolution-type system. I think it opens up more interesting narrative possibilities for the MC and players, especially because it makes killing corporate security personnel a character choice. So that change also applied to the Break Systems matrix move.
I look forward to seeing how the game goes for you! I'm definitely at the point where I'm thinking about how to codify my MCing and mission design techniques, so input from external MCs is especially useful!