Hello all,
just to bring this to an end. I gave up my initial plan to do everything with the Octatrack (was just so tempting to have all in one box)
I paired the Octa (with arranger activated) with my Digitakt with mute mode set to pattern and leaving mute activated (nice purple btw.
).
This gives me the ability to mute drums with my left hand (4 fingers at a time) and blending things in on the Octatrack with my right hand using the fader.
So drums are Digitakt now. Still not sure if I want them be direct or thru-track.
Thank´s for your input. Helped me thinking it over.
BTW: The Octatrack has one strange behavior when you set it master-mode for pattern change (PC) .
All my boxes are set to Auto-Channel 16. Octa is set to Autochannel 16 and to send PC on Autochannel. Does not work. 
You have to set it to channel 16. I don´t understand that and think this counter-intuitiv or a bug.
I´ve been through all my midi setup because I thought everything is ok with my Elektrons, not so.
Maybe worth a ticket, or can someone enlighten me with the deeper sense of that?