harmamusic:

The first option you described has the disadvantage that both H9s must use the same midi channel.

No. They could use a different channel even if the first H9 is set to midi thru. You could then have the MKIV set to channel 1 to talk to the first H9 set to CH1, while using CH2 for the second H9.

Midi channels are in fact often used to distinguish multiples instruments on a midi chain. Any midi devices set to pass thru will in fact pass all the channels. By definition the pass thru output is a "mirror" of the midi input.

I'll be back to you shortly about the 2nd way. But for now understand that the first way is easier to manage.

LA