I have both the PSR3000 & Korg PA50 on a double stand. Sometimes I midi them together, but mostly I use them independent. The Korg general sound and voices have more body and lower bass end than the 3K with the 3K sounding more thin.
However the differences when played independently but together have not cause me concern either both played through same external speaker system or even when played just using their own speakers.
The PA50 considering it's half the price of the 3K provides excellent quality.