Jim,

Sit down at your keyboard and record a very creative midi file, one that has lots of stereo effects and lasts a couple minutes. Put it in your keyboard, fire up both systems, play the midi file and walk throughout the room, listening carefully for those stereo sounds you created. Be objective, make sure that you can actually hear the left channel coming from the left, and the right channel sounds coming from the right. And, if you do some creative panning, you want to hear that as well. This will only take a few minutes, you can play the midi file at a modest level and it will not disturb anyone while they are eating.

If you think you hear stereo, go for two systems. If not, you already know what one system sounds like.

Hope everything works out well for you,

Gary