All the piano vioces sound so dull and unreal. How can I get a good piano sound out of this synth?

This is a sample based keyboard, so the starting point for your piano will be the base sample that is entered.

You can edit the voice however and store your modifications to the user voice setting.

THis can be done by going in to the voice and selecting enter. The manual will tell you what things can be changed and how.

From experience, you can make it a little brighter, but it won't sound like a concert grand when you are done.

If this is really important to you, have you considered adding something like the Alesis NanoPiano as an external module?