You wont be able to use the Minibrute as a controller that way. You have to go straight from minibrute to A4. Midi thru is really only a 2nd midi out, which means it is sending the same data that is being sent out the same machine’s midi out. It isnt a third type of midi signal flow.

The problem you run into here is that the A4 only has one midi in which makes you have to choose between controlling with Minibrute or Syncing with Octatrack.

Can the Minibrute be a controller through CV instead of Midi? Im not sure. Maybe someone else can answer that. If yes, it would free up the AR’s midi in port for the OT.

Another option might be a midi interface or splitter type device. Ive never used anything like this so maybe someone else can comment on that as well.
cheers