You have to set up your MOXF6 as an external device in Studio One. You have to set the MIDI channel that the MOXF6 is set to receive on correctly, then route the MIDI track in Studio One back out to your MOXF6.
See my example: In the first image below you can see that I set up my Yamaha TX-7 as an external device listening on MIDI channel 9 (because my TX-7 is configured to listen on MIDI channel 9). In the second image you can see that I have routed the instrument track out to my TX-7.