More thoughts:
1) You say "A MIDI clock is not possible, one can not set the tap tempo anymore."
You may or may not be able to use MIDIclock, but setting the tap tempo is pretty easy, either by a switch or MIDI. You can also enter a tempo value directly on H9Control.
2) There is a small problem using a CC to set the tempo directly – you would be limited to values below 127 BPM, unless you made the CC value (say) a quarter of the actual tempo. This would then mean you could set 120 BPM, but not (say) 122 BPM. Nothing is easy.
