KF, Yes each part can be assigned a different midi channel, and can be split to control your XD3..
You can adjust all the parameters on the leslie simulator[I think it is very good].
In fact I was able to duplicate my favorite N.I. B4 patches..

You can only split one of each group , for example , left hand bass[synth] with right hand organ and/or piano..You can layer all three[groups]..Midi can allow you to add more types of sounds for your splits and layers..your SXR board will act as the internal synth group.
Hope this helped.
I agree with your key feel opinion..