The reason you need high polyphony on the Yamaha is bc each voice is made up of up to four waveforms. That means that holding a four note chord with R1,2and3 would take up 48 sounds before we start dealing with the accompaniment waveforms. Also the polyphony counts all the way until the release fades out.

On the Korg are the voices that complex ie do they have 4 waveforms for each sounds?