I am using the old madiface with the new totalmixFX.
In most cases I do not need the monitor out at all, and it would be more clearly arranged if these main out could be included in the right order with all outputs, and not separately on the right.
So I would propose to include a "none" option in the "assign-main out" menu.

The second thing I am asking for is to being able to assign the main out on all available channels. I am aware that you had your thoughts by limiting it to 1-16 (necessary for higher samplerates), but for me this is very uncomfortable, and I am sure this can be changed quite easily.
Channels 63-64 are almost always not occupied by a mic input, and 1-16 are always used for mic input.
If working with an external mixer, and using my laptop as an external "tape machine" for recording and playing back, and at the same time being able to check the incoming channels in totalmix, channels 63-64 for monitoring would be necessary.

Thanks for reading,
Georg