This is aimed at Yamaha players who use mono systems, but it may apply to many more users, too.
As I continue to tweak, and customize my new PA4x for it's debut, later this month, I found a little gem that I'd forgotten about from years ago ... STRETCH tuning! Switching from Equal to Stretch tuning adds such life to the sound, and almost creates a wider, stereo-like fullness that really opens up the sound.
Maybe the stereo samples in the Yamaha line could benefit from this simple change, if the option is available?
I remember Fran Carango did this to a U series (?) keyboard back in the 80s and it was a noticeable improvement. Look into your edit pages, and see if it's a feature on your keyboard - I'd be very interested in hearing if it helps anyone!