For some reason new iPods will often by default transmit a Mono signal instead of a Stereo signal while using Airplay. If you hear fax sounds coming out of your Piano's speaker, and the piano doesn't play right, there's a good chance that this is the problem. Your piano needs a clean Left track for Audio and a clean right track for Piano Data. If the signal is transmitted in Mono, the two signals get mixed which in turn makes it impossible for the piano to play properly.

GO TO SETTINGS ON YOUR DEVICE...
MAKE SURE THAT MONO AUDIO IS OFF