Before you touch the keyboard I would recommend looking at your speaker system first. The onboard speakers are ok, but for serious use you would be better served with some Studio Reference Speakers for home use. If you play professionally then your PA must have a balanced frequency range, in other words, good High, Mid and Bass. Most modern budget systems (and some not so budget) miss out heavily on the mid range - Which why your Piano sounds thin. If you can borrow a pair of studio reference headphones to try you will see what I mean.

In the UK the two recommended systems are the Ketron PA and Solton Aart Sat. Our demonstrator also like Bose L1 but I like the B&O amps in the Ketron and Solton units.

I honestly believe only a few Ketron owners have ever heard their keyboards as Ketron intended, particularly Audya.