The controllable parameters of the audio tracks are listed on page C-2 of the OT’s manual.
You can control the volumes of the signals from inputs AB and CD if you are using Thru machines to monitor your external instruments. You can also control effects and track levels.
You would need to setup appropriate Scenes if you wanted MIDI control of the DIRect signal inputs.
All these controls use MIDI CC messages on the channels that are assigned to the tracks, so you need to ensure that your controller can send such messages.