I can just achieve one "extra voice" in the diatonic algorithm. When I pan over to the "B-voice" only the original signal is heard, no harmony.

I´m plugged in to input1 and output1. What am I doing wrong?

A few questions: 

– What version firmware are you running on your H9?

– Can you post a screen shot of your preset, or give us the parameter values? 

– If you are on the later firmware, what is your routing mode?