I am not a pianist like Bachus so my preference is the same as Fran's color board example. Whereas, any of my total boards are quite capable by themselves, once in a while I may take my BK-9 for my main, and maybe, the S910 for my top color board. and then, only for 3-4 hour dinner gigs. The placement is like Fran's with the second board up enough to reach the controls, and tilted.

I am not a button pusher by nature, and like to have variety at my fingertips for immediate use, and by using midi, I can interact any way I want.

However, usually I don't think it is worth the trouble except as above.