Not gonna be back in studio till tomorrow now, but having a quick dig into the manual I presume this is something I might have missed?:
Secondary function opens the MIDI CONFIGURATION menu. 38. [MIDI EXT] activates/deactivates KEYBOARD and DATA ENTRY knob MIDI control of external equipment.
EXTERNAL KEYBOARD MODE
Pressing [MIDI EXT] will turn the keyboard controls of the Analog Keys into an external MIDI keyboard con-
trolling other gear. The KEYBOARD keys, JOYSTICK, DATA ENTRY knobs and the LEVEL knob will be dedi-
cated to sending MIDI Out messages. Until deactivated, the Analog Keys synth and parameter settings will not
be affected by these controls, only the external MIDI gear. Press the key again to deactivate. Note that the inter-
nal sequencer and synth tracks will continue to work normally even while the external keyboard mode is active
I see also this thread: