I've been using Mainstage 2 with my trusty Motif ES7 for about a year now. I've hard to employ some "work-arounds" that may or not have been necessary, but seem to have solved the problems I encountered.
[b]Note: I"m connecting via MIDI-OUT to USB on the laptop (Motif USB is dead)[/b]
First problem I encountered was being unable to use all 4 sliders...tried many settings on the Motif but never got them to function properly. That's ok since my greater issue was lack of 9 drawbars...Easy solution was to get a Korg Nano and velcro it right above the screen. Gives me plenty of control of whatever parameters I want.
(I also have my Macbook with velcro on the left side)
Other issue I had was random volume messages being sent to the Laptop from the Master setup, which would reset all the custom fader settings I had set on my Mainstage patches. Solution I used : in Layout create a round knob, choose Number : 7, Type : Absolute, MIDI thru : Do not pass through
This prevented any volumes messages being sent from my Motif.
I haven't tried the FW16E, but that looks interesting... I have the Motif going into an Alesis Multimix FW, and laptop FW to the Alesis.
Lastly, shout out to my favorite organ plugin : VB3 - http://www.genuinesoundware.com/?a=showproduct&b=24
Adding MS to my rig had greatly expanded the sense of creativity I have with sounds and stop me from jumping ship to the Nord Stage, which everyone else in town seems to have done...