The audio side of the OT can have the MIDI i/o turned off, so that’s an option for you to look at, if you want to use the OT for midi recording and not play the OT audio tracks via the keyboard then set it up to ignore Note and CC, then enable the MIDI channels on the MIdi tracks and put the thru to use to feed the synth the keys - however, this will require cable switching or a merge at your synth to play the sequencer through teh OT out - or you’ll need a midi thru box after your keys to duplicate the keys and feed both, but it’ll still require a merge i think, if you want to retain maximum flexibility, plenty of recent threads about midi merge solutions