The first question about live gigging is who should be hearing the keyboard in stereo AND whether the venue has it's own PA.
If you're doing it for the audience, then a stereo combo amp won't do it for you. The two speakers are too close together for the audience to hear it as stereo. You really need to set up separate speakers on opposite sides of the stage. With luck, the venue already has those speakers in place, and sends them a stereo feed. At that point, just send the venue's PA a stereo feed from your keyboard and have them pan them hard left and hard right.
Otherwise you're talking about hauling around two sets of keyboard amps and speakers, etc., or maybe your own PA system. Depending on the style of music, this may or may not be worth it. If you're going for atmospheric music (think Pink Floyd, Kraftwerk, etc.) then you want to wash the audience in sound. Stereo is good. Quad is better. (Does anyone still make good quad live mixers?) But if you're playing bar band blues, then it's probably not worth the effort.
If it's just for you, it might be simpler to just get two hot spot monitors. Put them on each side of the keyboard, aimed at your head. The audience gets the keyboard amp, but you get the stereo separation you crave.
