It isn't so much that the PX-5S does things that the Kronos can't. I could very well use the Kronos as my only sound source. In fact, in the studio, I tend to use the PX-5S solely as a controller. But when I was designing some sounds for live use, I found that the MONO acoustic piano from the PX-5S sounded better than what I could get from the Kronos when played through my amp (a Motion Sound KT-80) competing in a loud blues/rock band. Now, if I played live in stereo or had a good powered PA speaker instead of the KT-80 or had time to program a good mono piano on the Kronos or played in a different band, maybe I'd configure it differently. So basically what I'm doing is sending program changes to the PX-5S to switch between acoustic piano and pure controller when I need it for playing rhodes/wurli sounds which come from the Kronos. And then I play organ and synth tones from the Kronos 61 keyboard because it feels more natural. The other benefit I get has to do with my amp and volume control. Since I am using the Kronos mainly for e.pianos and organs, I dirty up the sound a bit by running the L-main out (mono) through the amp's tube channel, while the PX-5S goes through the clean channel. Now, I could use the Kronos's individual outs to do the same thing, but anything run through the Kronos's individual outs bypass the main volume knob. This makes it really difficult to keep the organs, e.pianos, and a.pianos balanced. Whereas, I kind of have a feel for how to adjust the PX-5S and Kronos together to keep things under control. I want to emphasize that this is what works for me. The results have been great so far. It is awesome that we have instruments that are so flexible, even if it takes some time to tame them.