In my Pa500 the sound is modified acording to the way the sound is programmed, ie changing filter cut off (pad sounds), pitch (harmonica), modulation (flutes). In the Psr s900 nothing changes after sending the aftertouch message which I verified was sensed in the Midi receive chart. With my MS as a controller I can program the desired aftertouch effect for the internal sounds not for the external sounds (I use older 2.5 OS). In the same way using my Korg Tr as a controller no aftertouch effect is applied to the Psr either. May be Yamaha included the aftertouch (AT) receive function in the Psr line (with no AT keys) just for using external controllers which can send specific effects no "pure" AT messages.