I'm not sure I understand the question. You have to recognize for the Motif XF to communicate digitally with your computer it uses the FW16E to replace (key word: replace) the audio interface of your computer.

The audio of your computer can be routed to any of the outputs of the Motif XF (it is now your computer's audio interface). You have a 16-in/6-out audio interface for the computer.

Therefore if you want to do something with signal in the computer, it will not come out of the headphone jack of your computer, nor will not come out of the optical digital Output either. Reason: The FW16E is your audio interface, therefore audio is all routed via the FW16E.

You can choose between 3 Stereo pairs of outputs options with the FW16E (That is the 6-out portion of the interface).

Main L/R - you can route audio from the computer to the main left and right analog outputs on the back panel of the Motif XF
FW L/R - you can route audio from the computer to the FW left and right outputs - this can be returned to the XF's mixer where you can process it, or you can route it to the Motif XF's built-in sampler for recording
Asgn L/R - you can route audio from the computer to the assignable left and right outputs on the back panel of the Motif XF

If you opt to return audio to the Main L/R not only will it come out of the speakers connected to your Motif XF, it will arrive at the Motif XF Phones jack.
If you opt to use the FW L/R it travels through the XF's mixer before being combined with the main signal to the main L/R outputs
If you opt to use the Asgn L/R you are routing the signal discreetly to its own analog pair of outs.

You don't really say what it is you wish to accomplish - the Motif XF w/FW16E is your audio interface - if you need to route signal out you do so from the Motif XF.

Thanks Bad Mister

You answered my question. It really was about the Montage. You see right now I have my Motif XF connected to my Imac via FW16 and I routed the Digital Out of my Motif to an external digital recorder and then on to a DAC, amplification and passive monitors. It all works great. When I saw that the Montage does NOT have a Digital Out I was thinking of how I can keep my same set up with the Montage. I see now that I will have to route the Montage Audio out to an external A/D converter and then into my digital recorder.