When I spotted your thread, at first I thought you had in mind, splitting the Rhodes output onto two, say bass & treble zones. Because around 1980, there was a popular mod that went even one step further, three zones. (?!?) If I'm not mistook, the company that made this popular was Dyno My Piano, and lots of other shops copied their mod. BUT - that's not what you're looking for.
What you are looking for, if I'm not mistook, is a way to Y out into two amps, put effects on one and no effects on the other, and without loading down the piano's output so badly the tone turns to mush. Might look into Radial's "Big Shot" splitter. No effects loop, but you could place your effects on one of the output branches, meanwhile keep things nice & simple. One more benefit: one of the Big Shot's outputs is transformer coupled, which allows you to break the ground loop you encounter by Y'ing into two amps. With it you can operate both amps grounded for safety & not have the annoying hum from the ground loop.
If the Big Shot isn't quite the thing, maybe look into some of Radial's other problem solving device, or similar items from other companies. Here's a link: http://www.radialeng.com/product/bigshot-aby