Gary edited the Yamaha piano and it sounds really good. I just played it as it came from the factory, but I use some pretty intense e.q. on the entire keyboard with the PSR 900. You have to be sure and keep plenty of mids in the mix for the piano to sound good.
I don't have a problem at all with the SD5 piano sound, or the G70 sound. I don't do anything special, except to run both left and right leads to the Bose.
Maybe Gary will be of more help.
DonM