synth to stage piano MIDI

Hi I am wondering if this is possible:

I have a KORG PS60 synth and a KORG SP250 stage piano. The synth has no built in speakers but the stage piano does. I want to link up the two (I have MIDI cables) so that when I play the synth it outputs through the stage piano's speakers.

I have played around with it for a while and all I can do is get the synth to sound (through headphones) when playing the stage piano keys, or vice versa. I want the synth sound to be outputted through the stage piano's speakers.

The stage piano does not have a line in port (which would have been the easiest option).

Can someone advise me if this is possible, and if so, how to achieve it? Do I need an external box or something? Thanks a lot.

[This message has been edited by davebrackett (edited 11-02-2010).]

Midi does not transmit Audio signal...If your Piano does not have aux in (audio inputs)..You will not be able to do what you want..Your only alternative is to use an external powered speaker system..

ok thanks for your help. i will look at alternatives.