The Korg sound system (both PA60-AND-80)tends to break up with strong vocals, and dominant bass...even from a midi file. I could never get it more than about 3/4 of the total volume...and that was too much some times. The PSR2100 is not as full sounding, but the presence is better and the overall volume is percieved to be louder with no distortion.
The tone of the Korg is better, I think because of the auto loudness circuitry, but that probably causes the boomyness that distorts easily at louder volumes.