How about ensuring no channels are shared (clashing) between the OT and blofeld. I’m only tentatively putting that out there because I have a feeling OT will only pass midi out on channels that it has tracks assigned to, unless you use the thru, but I assume you also want the SP16 to control the OT in some ways?
Midi splitter or even a switch could solve this, but probably not what you wanted to hear.
I know I have often intended to setup things a lot like you, and wondered beforehand about the slightly inflexible thru functionality of the OT, but maybe I never quite got there (too busy step sequencing the blofeld and sampling it back in, rather than doing any live playing over it)
Will definitely setup this way next time I have a chance - but pretty sure it’s the channel-tracks assignments and autochannel settings that’ll make or break it.
If you set a midi track to the channel you want to play on the blofeld, and it’s not the auto channel or assigned to any other track (audio or midi), then you send notes from sp16!on that channel while that track is active. That would be my starting point
Or maybe the OT thru socket will pass anything that is received on unassigned channels, with the downside that the blofeld will then get nothing from the OT’s sequencer. Unless you merge
Then there’s clock to think about…
enough thinking aloud - I need to try it & Will let you know unless ‘someone else’ steps in with the gear at hand