Good keyboards can sound very much like a good piano, even a high-end concert piano. Wifey's keyboard sounds every bot as good as her small grand piano.
But that also means good amplification, etc... and sometimes means stereo amplification, speaker separation, etc. Not unsolvable, except for maybe extreme speaker separation depending on boat size and shape.
You'll know this, but the "feel of the keys" (weighted, etc.) and a full-length (88 keys) keyboard are generally important for serious work.
When wifey shopped, she ended up eventually focusing on Roland, Korg, Yamaha, and... hmmm... another brand I can't remember right now... I suspect almost all the good ones from each of those companies are pretty impressive.
-Chris