Yes, I tested briefly yesterday night with not much time but it works.
At first, I couldn’t make the 3 machines change pattern at the same time, but the thing was I had to set Digitakt to send program changes to a specific midi channel and then configure Syntakt and Digitone to receive program changes from this midi channel.
I noticed by jamming only 10 minutes that you have to be very careful about what machine is in live recording mode, which track is selected in the machine you want to input notes and be very careful to not enter notes on Midi tracks 1 or 2 of Digitakt, but let them go straight into Syntakt or Digitone sequencer activating live recording mode on the desired machine.
But it works. And Keystep responds to tempo set from Digitakt, so you can send internal Keystep sequencer to any MIDI track and you can record arpeggiated melodies played from Keystep into any of the 3 machines.
Cheers to all of you!