at one time i had tyros on the bottom,korg pa80 ontop. and a roland va76 on the right side. it turned out not to practical for me.
alot of investment of money,set up time only to be paid the same as when i was playing the old korg i5 and the yamaha psr 1000. plus my singer had 2 keyboards.in the 80s i had a b3,rhodes, moog, stacked then a wurly,arp and elka string machine on the right. i found that using 2 keyboards gave me a little more flexabiity, but not enough to warrent that type of investment. i guess it's a matter of personal preference and how you use them.