I have X2 and X3 installed on the same machine.
In X3, "DimsionPro x64 - 2" is listed on the list of MIDI inputs. It is not in X2. It is also listed as a MIDI output option. This is confusing.
Why this change? What does this mean? Can I remove this as an input option?
Thanks in advance.

Bump.

What is odd about it being listed as a MIDI input? How would you route MIDI to it otherwise?
 
 

He means that Dim Pro is showing up as a MIDI source, as if it were a keyboard or other MIDI controller. This is because Dim Pro can indeed output MIDI in the form of groove programs. I haven't ever used the feature myself, only read about it in the Dim Pro help file.

Right-click Dim Pro in the synth rack, and uncheck Enable MIDI Output to remove it from the list of available inputs to MIDI tracks.