Hi Terri,
What do you mean by synced? If you have the stereo analog outs from your keyboard plugged into two input channels on your 788, you should be all set.
If you are using the S/PDif as your stereo audio digital transfer method, the just make sure the Keyboard is set to send the digital signal at 44.1Khz. The 788 is already expecting a 44.1Khz digital signal, so that is all you probably need to do.