And again someone tripped over the octave naming scheme. 
The MIDI standard contains no fixed naming scheme for octaves. So some devices call their lowest MIDI note (decimal value=0) C-2, others name it C-1 or C0.
The Digitakt uses C0.
So the effect of being one or two octaves off, is just a matter of how the octaves are named (which was never standardized).
When sending MIDI notes between different devices match their decimal note values and not how these notes are named on the devices.