Piano sounds are plunky. somewhat like a mirimba or guitar. Any ideas how to edit the sound to be more like an acoustical piano?
It sounds like you have an issue with your sound system setup. I've used similar keyboard amps and portable PAs like Roland and they all performed poorly. They may be tolerable for live and outdoor applications but they suck in the studio. What you need is a descent pair of studio monitors to achieve the sonic clarity you are desiring and the Yamaha S90 ES deserves.