Thanks for sharing this.

It's quite close and all sound very good but I think but at a push I'd say the SX900 had the warmest fuller/cleaner sound, the S970 was the loudest/weightiest/punchiest and the Korg was a little bit on the light/thin side.
Ketron SD60, Ketron SD7, Korg Pa1000, Yamaha SX900, Yamaha Tyros4