Yes! I just got it setup yesterday. Spent some time doing some major modifications to my layout. The trick is that you need to make an onscreen control for every encoder. If you are using relative mode for the encoders (which I strongly recommend), make sure the onscreen encoders are set to relative as well, and have their mode set to "Sign Magnitude", which is the method the Keylab uses. Through this, Mainstage will translate this very "un-standard-ish" data into something that all synths can understand.
I don't plan on using the second bank of encoders, but I will use the second bank of faders, so I saved myself some hastle by setting the second bank of encoders to the same CCs as the first. That way I only need to have 10 onscreen nobs instead of 20.
If screen real estate is at a premium, make the onscreen controllers fairly small. I have ten encoders vertically lined up on one side of my layout from top to bottom of the screen, and they don't take up much space. Faders I made REALLY tiny, as I figure I won't have to visually look at them, since I have actual tactile reference. I made one normal set of 9 faders, and then I used Mainstages built in "organ drawbars" fader group (and shrunk it down), for bank B.
All this takes some time, but if you set it up intuitively and make it look nice, it'll really pay off in the long run.
