Okay, I tested the MIDI Clock situation in several setups, and the only thing that seems to work reliably is the CKIN out.
I tested it as a Clock out using USB to my Endorphines Shuttle Control which I did not get to work. Also I can not make it work using my Mac. In both cases I was able to receive note on/off via MIDI, but not the clock.
Then I tried to use my Prophet XL to send clock via MIDI DIN to the arches. Did not work.
Then I tried to use my Waldorf kb37 to send clock via MIDI DIN to the arches. Did not work.
Needless to say that the arches is pretty much useless in a larger setup unless it can be integrated as a master clock or as a slave using either MIDI DIN or MIDI USB.
When will be the next firmware release fixing at least all the clock issues? Without a working clock the upcoming arpeggiater functions will be worthless to me, so this is basic functionality that we need to be able to rely on.